The problem of philosophy arises as soon as one begins to think of a relation to the world. Religion is not philosophy. However, the religion of reason, by virtue of its share in reason, has at least some kinship with philosophy. It is therefore not surprising that this share in reason, akin to that of philosophy, begins to stir within religion, starting, it would seem, with its concept of God.
Hermann Cohen, Religion of Reason out of the Sources of Judaism, Simon Kaplan, tr. Scholars Press (Atlanta, GA: 1995) p. 36. I am only just now getting the chance to read through Cohen's classic of Jewish philosophy from cover to cover; very interesting so far. Cohen, despite not being read much in the English-speaking world today, was a major German Neo-Kantian, one of the most important philosophers in the world in the lead-up to World War I, and certainly the most important Jewish philosopher between Mendelssohn and our day. Religion of Reason presents a Kantian interpretation of Judaism, in which Judaism provides a relatively pure vocabulary for talking about ethical monotheism and its implications. One of Cohen's most important arguments is that ethical monotheism requires a form of messianism, in terms of postulating the possibility of a Messianic Age, a future ethical community of humanity united by a moral ideal.