Einstein was a deeply religious individual and wrote extensively about the philosophy of religion. Although he was born a Jew, his family was not particularly observant, choosing not to follow traditional dietary laws or attend religious services. They sent Albert to a Catholic public primary school at age six, though he did receive instruction in his own religion from a distant relative, as such instruction was compulsory in the state of Bavaria. When Einstein moved on to the Luitpold Gymnasium, he received the two hours of religious instruction per week that the school offered its Jewish pupils. Einstein studied the Ten Commandments, biblical history, and the rudiments of Hebrew grammar. Although he went through a strong religious phase as a child, his acquaintance with Max Talmud, the poor Jewish medical student who joined the Einstein family for a weekly meal, soon weakened his regard for traditional religion. Talmud recommended philosophical and popular scientific books that led Einstein to doubt the religious precepts he had been taught in school. Einstein began questioning the veracity of the Bible and discontinued the preparation for his bar mitzvah. Some biographers point to this early religious skepticism as the source of Einstein's freedom of thought and intellectual independence as a scientist; in any case, it is clear that his defiance of authority was to remain an important aspect of his thinking and his personality for the rest of his life.
Einstein remained indifferent to religious conventions and precepts throughout his adult life. His first wife, Mileva Maric, was a member of the Greek Orthodox Church, and the marriage took place without the presence of a rabbi or a priest. Although the religious difference caused both sets of parents to object to the marriage, it did not trouble Einstein: he did not want his children to receive any form of religious instruction and the couple practiced no formal religion in their home. Additionally, Einstein asked to be cremated rather than buried in the Jewish tradition. Thus his disregard for religious rituals lasted his whole life.
Yet in spite of his disdain for religious instruction in accordance with any particular denominational tradition, Einstein nonetheless always maintained a pious sentiment of inspired religious devotion. He identified very closely with the seventeenth-century Dutch Jewish philosopher Baruch Spinoza, who rejected the traditional theistic concept of God in favor of an impersonal cosmic order. Spinoza believed that the universe is governed by a mechanical and mathematical order such that all events in nature occur according to immutable laws of cause and effect. He held that God is devoid of ethical properties and therefore does not reward or punish human behavior. Einstein, who studied Spinoza's Ethics in Bern with his friends of the Olympia Academy, was drawn to this philosopher because they shared a love of solitude and the experience of having rejected their Jewish religious tradition. Einstein also joined with Spinoza in denying the existence of a personal God and an unrestricted determinism. Yet Einstein was not an atheist; indeed, he is often quoted as having said, "Science without religion is lame, religion without science is blind." Though he denied any sort of personal God, he shared Spinoza's faith in a superior intelligence that reveals itself in the beauty of nature.
Einstein was also a proponent of Schopenhauer's idea of a "cosmic religious feeling," in which true religiosity is constituted simply by a sense of wonder and awe for the world. Einstein claimed that although science and religion as traditionally conceived were antagonistic, the religiosity of cosmic religious feeling is actually the strongest motive for scientific research; only those who feel a rapturous amazement at the harmony of nature can delve into her secrets. He argued that Kepler and Newton were inspired by a deep belief in the rationality of the universe and a faith in universal causation. Einstein thus understood science and religion to function in concert with one another.
Another aspect of Einstein's religious life was his relationship to the Jewish people. Although he did not observe Jewish traditions, Einstein appreciated the love of truth and justice that he saw as constituting the core of Judaism. He claimed that Jews have been united throughout the centuries by a reverence for truth, a democratic ideal of social justice, and a desire for personal independence. In Einstein's view, the greatest Jews, including Moses, Spinoza, and Marx, were those who sacrificed themselves for these ideals. Above all, Einstein believed that Judaism involves a strong sense of the sanctity of life and a rejection of all superstition. He contended that the creation of a Jewish state would preserve these values for the world. Einstein thus had a cultural and intellectual vision for Israel, rather than a political one. The greatest danger posed by anti-Semitism, he believed, was the threat it posed to the survival of Jewish ideals; thus Israel must serve as a region sheltered from Europe's deep-seated anti-Semitism, must constitute a seat of modern intellectual life and a spiritual center for the Jews.