When Nebuchadnezzar took Jerusalem and deported its elite, and then burned the temple after a second revolt, he removed at a stroke everything the religion of Judah had been organised around. There was one lawful place of sacrifice and it was rubble. There was a dynasty promised in perpetuity and its last king was blinded and taken away. There was a land held by covenant and the covenant people were several hundred miles east of it.
What survived was what could be carried. Practices that require no altar became central: the sabbath, circumcision, the reading and study of texts, dietary distinctions, and prayer. Whether the institution of the synagogue itself begins in the exile is often asserted and cannot be demonstrated from the sources, but the shift of religious weight from sacrifice to assembly and text is visible in the material of this period.
The theological consequence was as large. A defeated people whose god had been humiliated could conclude that the victor's gods were stronger. The prophetic literature of the exile draws the opposite conclusion: the catastrophe was their own God's doing, a judgment rather than a defeat, and the gods of Babylon are nothing at all. The insistence that there is one God, and that the others do not merely rank lower but do not exist, is stated in these texts with a clarity not found earlier.