In regard to God, the Reform movement has always officially maintained a theistic stance, affirming the belief in a personal God.^[7] Despite this official position, some voices among the spiritual leadership have approached religious and even secular humanism. This tendency has grown since the mid-20th century among both clergy and constituents, leading to broader, dimmer definitions of the concept.

Early Reform thinkers in Germany clung to this precept;^[8] the 1885 Pittsburgh Platform described the "One God... The God-Idea as taught in our sacred Scripture" as consecrating the Jewish people to be its priests. It was grounded on a wholly theistic understanding, although the term "God-idea" was excoriated by outside critics. So was the 1937 Columbus Declaration of Principles, which spoke of "One, living God who rules the world".^[9] Even the 1976 San Francisco Centenary Perspective, drafted at a time of great discord among Reform theologians, upheld "the affirmation of God... Challenges of modern culture have made a steady belief difficult for some. Nevertheless, we ground our lives, personally and communally, on God's reality."^[10] The 1999 Pittsburgh Statement of Principles declared the "reality and oneness of God". British Liberal Judaism affirms the "Jewish conception of God: One and indivisible, transcendent and immanent, Creator and Sustainer".

The basic tenet of Reform theology is a belief in a continuous, or progressive, revelation,^[11][12] occurring continuously and not limited to the theophany at Sinai, the defining event in traditional interpretation. According to this view, all holy scripture of Judaism, including the Torah, were authored by human beings who, although under divine inspiration, inserted their understanding and reflected the spirit of their consecutive ages. All the People of Israel are a further link in the chain of revelation, capable of reaching new insights: religion can be renewed without necessarily being dependent on past conventions. The chief promulgator of this concept was Abraham Geiger, generally considered the founder of the movement. After critical research led him to regard scripture as a human creation, bearing the marks of historical circumstances, he abandoned the belief in the unbroken perpetuity of tradition derived from Sinai and gradually replaced it with the idea of progressive revelation.

As in other liberal denominations, this notion offered a conceptual framework for reconciling the acceptance of critical research with the maintenance of a belief in some form of divine communication, thus preventing a rupture among those who could no longer accept a literal understanding of revelation. No less importantly, it provided the clergy with a rationale for adapting, changing and excising traditional mores and bypassing the accepted conventions of Jewish Law, rooted in the orthodox concept of the explicit transmission of both scripture and its oral interpretation. While also subject to change and new understanding, the basic premise of progressive revelation endures in Reform thought.^[2][13]

In its early days, this notion was greatly influenced by the philosophy of German idealism, from which its founders drew much inspiration: belief in humanity marching toward a full understanding of itself and the divine, manifested in moral progress towards perfection. This highly rationalistic view virtually identified human reason and intellect with divine action, leaving little room for direct influence by God. Geiger conceived revelation as occurring via the inherent "genius" of the People Israel, and his close ally Solomon Formstecher described it as the awakening of oneself into full consciousness of one's religious understanding. The American theologian Kaufmann Kohler also spoke of the "special insight" of Israel, almost fully independent from direct divine participation, and English thinker Claude Montefiore, founder of Liberal Judaism, reduced revelation to "inspiration", according intrinsic value only to the worth of its content, while "it is not the place where they are found that makes them inspired". Common to all these notions was the assertion that present generations have a higher and better understanding of divine will, and they can and should unwaveringly change and refashion religious precepts.^[2]

In the decades around World War II, this rationalistic and optimistic theology was challenged and questioned. It was gradually replaced, mainly by the Jewish existentialism of Martin Buber and Franz Rosenzweig, centered on a complex, personal relationship with the creator, and a more sober and disillusioned outlook.^[14] The identification of human reason with Godly inspiration was rejected in favour of views such as Rosenzweig's, who emphasized that the only content of revelation is it in itself, while all derivations of it are subjective, limited human understanding. However, while granting higher status to historical and traditional understanding, both insisted that "revelation is certainly not Law giving" and that it did not contain any "finished statements about God", but, rather, that human subjectivity shaped the unfathomable content of the Encounter and interpreted it under its own limitations. The senior representative of postwar Reform theology, Eugene Borowitz, regarded theophany in postmodern terms and closely linked it with quotidian human experience and interpersonal contact. He rejected the notion of "progressive revelation" in the meaning of comparing human betterment with divine inspiration, stressing that past experiences were "unique" and of everlasting importance. Yet he stated that his ideas by no means negated the concept of ongoing, individually experienced revelation by all.^[12]

Reform Judaism emphasizes the ethical facets of the faith as its central attribute, superseding the ceremonial ones. Reform thinkers often cited the Prophets' condemnations of ceremonial acts, lacking true intention and performed by the morally corrupt, as testimony that rites have no inherent quality. Geiger centered his philosophy on the Prophets' teachings (he had already named his ideology "Prophetic Judaism" in 1838), regarding morality and ethics as the stable core of a religion in which ritual observance transformed radically through the ages. However, practices were seen as a means to elation and a link to the heritage of the past, and Reform generally argued that rituals should be maintained, discarded or modified based on whether they served these higher purposes. This stance allowed a great variety of practice both in the past and the present. In "Classical" times, personal observance was reduced to little beyond nothing. The postwar "New Reform" lent renewed importance to practical, regular action as a means to engage congregants, abandoning the sanitized forms of the "Classical".

Another key aspect of Reform doctrine is the personal autonomy of each adherent, who may formulate their own understanding and expression of their religiosity. Reform is unique among all Jewish denominations in placing the individual as the authorized interpreter of Judaism.^[15] This position was originally influenced by Kantian philosophy and the great weight it lent to personal judgement and free will. This highly individualistic stance also proved one of the movement's great challenges, for it impeded the creation of clear guidelines and standards for positive participation in religious life and definition of what was expected from members.

The notion of autonomy coincided with the gradual abandonment of traditional practice (largely neglected by most members, and the Jewish public in general, before and during the rise of Reform) in the early stages of the movement. It was a major characteristic during the "Classical" period, when Reform closely resembled Protestant surroundings. Later, it was applied to encourage adherents to seek their own means of engaging Judaism. "New Reform" embraced the criticism levied by Rosenzweig and other thinkers at extreme individualism, laying a greater stress on community and tradition. Though by no means declaring that members were bound by a compelling authority of some sort – the notion of an intervening, commanding God remained foreign to denominational thought. The "New Reform" approach to the question is characterized by an attempt to strike a mean between autonomy and some degree of conformity, focusing on a dialectic relationship between both.^[16]

The movement never entirely abandoned halachic (traditional jurisprudence) argumentation, both due to the need for precedent to counter external accusations and the continuity of heritage. ^{[citation needed]} Instead, the movement had largely made ethical considerations or the spirit of the age the decisive factor in determining its course. The German founding fathers undermined the principles behind the legalistic process, which was based on a belief in an unbroken tradition through the ages merely elaborated and applied to novel circumstances, rather than subject to change. Rabbi Samuel Holdheim advocated a particularly radical stance, arguing that the halachic Law of the Land is Law principle must be universally applied and subject virtually everything to current norms and needs, far beyond its weight in conventional Jewish Law.

While Reform rabbis in 19th-century Germany had to accommodate conservative elements in their communities, at the height of "Classical Reform" in the United States, halakhic considerations could be virtually ignored and Holdheim's approach embraced. In the 1930s and onwards, Rabbi Solomon Freehof and his supporters reintroduced such elements, but they too regarded Jewish Law as too rigid a system. Instead, they recommended that selected features will be readopted and new observances established in a piecemeal fashion, as spontaneous minhag (custom) emerging by trial and error and becoming widespread if it appealed to the masses. The advocates of this approach also stress that their responsa are of non-binding nature, and their recipients may adapt them as they see fit.^[17] Freehof's successors, such as Rabbis Walter Jacob and Moshe Zemer, further elaborated the notion of "Progressive Halakha" along the same lines.

Reform sought to accentuate and greatly augment the universalist traits in Judaism, turning it into a faith befitting the Enlightenment ideals ubiquitous at the time it emerged. The tension between universalism and the imperative to maintain uniqueness characterized the movement throughout its entire history. Its earliest proponents rejected Deism and the belief that all religions would unite into one, and it later faced the challenges of the Ethical movement and Unitarianism. Parallel to that, it sought to diminish all components of Judaism that it regarded as overly particularist and self-centered: petitions expressing hostility towards gentiles were toned down or excised, and practices were often streamlined to resemble surrounding society. "New Reform" laid a renewed stress on Jewish particular identity, regarding it as better suiting popular sentiment and need for preservation.

One major expression of that, which is the first clear Reform doctrine to have been formulated, is the idea of universal Messianism. The belief in redemption was unhinged from the traditional elements of return to Zion and restoration of the Temple and the sacrificial cult therein, and turned into a general hope for salvation. This was later refined when the notion of a personal Messiah who would reign over Israel was officially abolished and replaced by the concept of a Messianic Age of universal harmony and perfection. The considerable loss of faith in human progress around World War II greatly shook this ideal, but it endures as a precept of Reform.^[18]

Another key example is the reinterpretation of the election of Israel. The movement maintained the idea of the Chosen People of God, but recast it in a more universal fashion: it isolated and accentuated the notion (already present in traditional sources) that the mission of Israel was to spread among all nations and teach them divinely-inspired ethical monotheism, bringing them all closer to the Creator. One extreme "Classical" promulgator of this approach, Rabbi David Einhorn, substituted the lamentation on the Ninth of Av for a celebration, regarding the destruction of Jerusalem as fulfilling God's scheme to bring his word, via his people, to all corners of the earth. Highly self-centered affirmations of Jewish exceptionalism were moderated, although the general notion of "a kingdom of priests and a holy nation" retained. On the other hand, while embracing a less strict interpretation compared to the traditional one, Reform also held to this tenet against those who sought to deny it. When secularist thinkers like Ahad Ha'am and Mordecai Kaplan forwarded the view of Judaism as a civilization, portraying it as a culture created by the Jewish people, rather than a God-given faith defining them, Reform theologians decidedly rejected their position – although it became popular and even dominant among rank-and-file members. Like the Orthodox, they insisted that the People Israel was created by divine election alone, and existed solely as such.^[19] The 1999 Pittsburgh Platform and other official statements affirmed that the "Jewish people is bound to God by an eternal b'rit, covenant".

As part of its philosophy, Reform Judaism anchored reason in divine influence, accepted scientific criticism of hallowed texts and sought to adapt Judaism to modern notions of rationalism. Judaism was viewed by Enlightenment thinkers both as irrational and an import from ancient middle-eastern pagans. The only perceived form of retribution for the wicked, if any, was the anguish of their soul after death, and vice versa, bliss was the single accolade for the spirits of the righteous. Angels and heavenly hosts were also deemed a foreign superstitious influence, especially from early Zoroastrian sources, and denied.^[20][21] Notions of afterlife according to Enlightenment thinkers were given to be reduced merely to the immortality of the soul, while the founding thinkers of Reform Judaism, like Montefiore, all shared this belief, the existence of a soul became harder to cling to with the passing of time. In the 1980s, Borowitz could state that the movement had nothing coherent to declare in the matter. The various streams of Reform still largely, though not always or strictly, uphold the idea.^[22] The 1999 Pittsburgh Statement of Principles, for example, used the somewhat ambiguous formula "the spirit within us is eternal".^[23]

The first and primary field in which Reform convictions were expressed was that of prayer forms. From its beginning, Reform Judaism attempted to harmonize the language of petitions with modern sensibilities and what the constituents actually believed in. Jakob Josef Petuchowski, in his extensive survey of Progressive liturgy, listed several key principles that defined it through the years and many transformations it underwent. The prayers were abridged, whether by omitting repetitions, excising passages or reintroducing the ancient triennial cycle for reading the Torah; vernacular segments were added alongside or instead of the Hebrew and Aramaic text, to ensure the congregants understood the petitions they expressed; and some new prayers were composed to reflect the spirit of changing times. But chiefly, liturgists sought to reformulate the prayerbooks and have them express the movement's theology. Blessings and passages referring to the coming of the Messiah, return to Zion, renewal of sacrificial practices, resurrection of the dead, reward and punishment and overt particularism of the People Israel were replaced, recast or excised altogether.

In its early stages, when Reform Judaism was more a tendency within unified communities in Central Europe than an independent movement, its advocates had to practice considerable moderation, lest they provoke conservative animosity. German prayerbooks often relegated the more contentious issues to the vernacular translation, treating the original text with great care and sometimes having problematic passages in small print and untranslated. When institutionalized and free of such constraints, it was able to pursue a more radical course. In American "Classical" or British Liberal prayerbooks, a far larger vernacular component was added and liturgy was drastically shortened, and petitions in discord with denominational theology eliminated.

"New Reform", both in the United States and in Britain and the rest of the world, is characterized by larger affinity to traditional forms and diminished emphasis on harmonizing them with prevalent beliefs. Concurrently, it is also more inclusive and accommodating, even towards beliefs that are officially rejected by Reform theologians, sometimes allowing alternative differing rites for each congregation to choose from. Thus, prayerbooks from the mid–20th century onwards incorporated more Hebrew, and restored such elements as blessing on phylacteries. More profound changes included restoration of the Gevorot benediction in the 2007 Mishkan T'filah, with the optional "give life to all/revive the dead" formula. The CCAR stated this passage did not reflect a belief in Resurrection, but Jewish heritage. On the other extreme, the 1975 Gates of Prayer substituted "the Eternal One" for "God" in the English translation (though not in the original), a measure that was condemned by several Reform rabbis as a step toward religious humanism.^[24]

During its formative era, Reform was oriented toward lesser ceremonial obligations. In 1846, the Breslau rabbinical conference abolished the second day of festivals; during the same years, the Berlin Reform congregation held prayers without blowing the Ram's Horn, phylacteries, mantles or head covering, and held its Sabbath services on Sunday. In the late 19th and early 20th century, American "Classical Reform" often emulated Berlin on a mass scale, with many communities conducting prayers along the same style and having additional services on Sunday. An official rescheduling of Sabbath to Sunday was advocated by Kaufmann Kohler for some time, though he retracted it eventually. Religious divorce was declared redundant and the civil one recognized as sufficient by American Reform in 1869, and in Germany by 1912; the laws concerning dietary and personal purity, the priestly prerogatives, marital ordinances and so forth were dispensed with, and openly revoked by the 1885 Pittsburgh Platform, which declared all ceremonial acts binding only if they served to enhance religious experience. From 1890, converts were no longer obligated to be circumcised. Similar policy was pursued by Claude Montefiore's Jewish Religious Union, established at Britain in 1902. The Vereinigung für das Liberale Judentum in Germany, which was more moderate, declared virtually all personal observance voluntary in its 1912 guidelines.

"New Reform" saw the establishment and membership lay greater emphasis on the ceremonial aspects, after the former sterile and minimalist approach was condemned as offering little to engage in religion and encouraging apathy. Numerous rituals became popular again, often after being recast or reinterpreted, though as a matter of personal choice for the individual and not an authoritative obligation. Circumcision or Letting of Blood for converts and newborn babies became virtually mandated in the 1980s; ablution for menstruating women gained great grassroots popularity at the turn of the century, and some synagogues built mikvehs (ritual baths). A renewed interest in dietary laws (though by no means in the strict sense) also surfaced at the same decades, as were phylacteries, prayer shawls and head coverings. Reform is still characterized by having the least service attendance on average:^[25] for example, of those polled by Pew in 2013, only 34% of registered synagogue members (and only 17% of all those who state affinity) attend services once a month and more.^[26]

The Proto-Reform movement did pioneer new rituals. In the 1810s and 1820s, the circles (Israel Jacobson, Eduard Kley and others) that gave rise to the movement introduced confirmation ceremonies for boys and girls, in emulation of parallel Christian initiation rite. These soon spread outside the movement, though many of a more traditional leaning rejected the name "confirmation". In the "New Reform", Bar Mitzvah largely replaced it as part of the re-traditionalization, but many young congregants in the United States still perform one, often at Shavuot. Confirmation for girls eventually developed into the Bat Mitzvah, now popular among all except strictly Orthodox Jews.

Some branches of Reform, while subscribing to its differentiation between ritual and ethics, chose to maintain a considerable degree of practical observance, especially in areas where a conservative Jewish majority had to be accommodated. Most Liberal communities in Germany maintained dietary standards and the like in the public sphere, both due to the moderation of their congregants and threats of Orthodox secession. A similar pattern characterizes the Movement for Reform Judaism in Britain, which attempted to appeal to newcomers from the United Synagogue, or to the Israel Movement for Reform and Progressive Judaism (IMPJ) in Israel.

Its philosophy of continuous revelation made Progressive Judaism, in all its variants, much more able to embrace change and new trends than any of the other major denominations.

Reform Judaism is considered to be the first major Jewish denomination to adopt gender equality in religious life^{[citation needed]}. As early as 1846, the Breslau conference announced that women must enjoy identical obligations and prerogatives in worship and communal affairs, though this decision had virtually no effect in practice. Lily Montagu, who served as a driving force behind British Liberal Judaism and WUPJ, was the first woman in recorded history to deliver a sermon at a synagogue in 1918, and set another precedent when she conducted a prayer two years later. Regina Jonas, ordained in 1935 by later chairman of the Vereinigung der liberalen Rabbiner Max Dienemann, was the earliest known female rabbi to officially be granted the title. In 1972, Sally Priesand was ordained by Hebrew Union College, which made her the first female rabbi of the US ordained by a rabbinical seminary, and the second formally ordained female rabbi in Jewish history, after Regina Jonas.^[27][28][29] Reform also pioneered family seating, an arrangement that spread throughout American Jewry but was only applied in continental Europe after World War II. Egalitarianism in prayer became universally prevalent in the WUPJ by the end of the 20th century.

Religious inclusion for LGBT people and ordination of LGBT rabbis were also pioneered by the movement. Intercourse between consenting adults was declared as legitimate by the Central Conference of American Rabbis (CCAR) in 1977, Hebrew Union College - Jewish Institute of Religion accepted its first open LGBTQ students in 1990 (Leslie Bergson, Stephen Roberts and Burt Schuman) and the CCAR openly gay clergy were admitted in 1990.^[30][31][32] Same-sex marriage was sanctioned by the year 2000.^[33] In 2015, the URJ adopted a Resolution on the Rights of Transgender and Gender Non-Conforming People, urging clergy and synagogue attendants to actively promote tolerance and inclusion of such individuals.^[34]

American Reform, especially, turned action for social and progressive causes into an important part of religious commitment. From the second half of the 20th century, it employed the old rabbinic notion of Tikkun Olam, "repairing the world", as a slogan under which constituents were encouraged to partake in various initiatives for the betterment of society. The Religious Action Center of Reform Judaism became an important lobby in service of progressive causes such as the rights of minorities. Tikkun Olam has become the central venue for active participation for many affiliates, even leading critics to negatively describe Reform as little more than a means employed by Jewish liberals to claim that commitment to their political convictions was also a religious activity and demonstrates fealty to Judaism. Dana Evan Kaplan stated that "Tikkun Olam has incorporated only leftist, socialist-like elements. In truth, it is political, basically a mirror of the most radically leftist components of the Democratic Party platform, causing many to say that Reform Judaism is simply 'the Democratic Party with Jewish holidays'."^[35] In Israel, the Religious Action Center is very active in the judicial field, often using litigation both in cases concerning civil rights in general and the official status of Reform Judaism within the state, in particular.^[36]

While opposed to interfaith marriage in principle, officials of the major Reform rabbinical organisation, the Central Conference of American Rabbis (CCAR), estimated in 2012 that about half of their rabbis partake in such ceremonies. The need to cope with this phenomenon – 80% of all Reform-raised Jews in the United States wed between 2000 and 2013 were intermarried^[37] – led to the recognition of patrilineal descent: all children born to a couple in which a single member was Jewish, whether mother or father, was accepted as a Jew on condition that they received corresponding education and committed themselves as such. Conversely, offspring of a Jewish mother only are not accepted if they do not demonstrate affinity to the faith. A Jewish status is conferred unconditionally only on the children of two Jewish parents.

This decision was taken by the British Liberal Judaism in the 1950s. The North American Union for Reform Judaism (URJ) accepted it in 1983, and the British Movement for Reform Judaism affirmed it in 2015. The various strands also adopted a policy of embracing the intermarried and their spouses. British Liberals offer "blessing ceremonies" if the child is to be raised Jewish, and the MRJ allows its clergy to participate in celebration of civil marriage, though none allow a full Jewish ceremony with chupah and the like. In American Reform, 17% of synagogue-member households have a converted spouse, and 26% an unconverted one.^[38] Its policy on conversion and Jewish status led the WUPJ into conflict with more traditional circles, and a growing number of its adherents are not accepted as Jewish by either the Conservative or the Orthodox. Outside North America and Britain, patrilineal descent was not accepted by most. As in other fields, small WUPJ affiliates are less independent and often have to deal with more conservative Jewish denominations in their countries, such as vis-à-vis the Orthodox rabbinate in Israel or continental Europe.

Conversion within Reform Judaism has been seen as controversial by the Orthodox and Masorti sects. Due to the Reform movement's progressive views on what it means to be a Jew, the conversion process has been criticized and often unrecognized by more conservative sects, yet conversions through the Reform movement are legally recognized by the Israeli government and thus entitled to citizenship under the Law of Return.^[39]

Converts through Reform Judaism are accepted based on their sincerity, regardless of their background or previous beliefs. Studying with a rabbi is the norm and can take anywhere from several months to several years. The process focuses on participation in congregational activities and observation of holidays and Halakha. Conversions are finalized with a meeting of the Beit Din and usually a Brit Milah and a Tevilah, though the extent to which the practice of Brit Milah is observed varies from country to country.^[40] Furthermore, the acceptance of Reform converts by other sects is rare, with many Orthodox and Masorti temples rejecting Reform Converts.