At what point in biblical history did the fundamental pattern of jewish experience emerge, and what shape did it take

The fundamental pattern of the Jewish experience is a pattern of exile and return.  

I would say the first example of that in biblical history was the experience of the people of Israel growing into a nation within Egypt, being enslaved by the Egyptians, then being led by Moses to return to the land where the patriarchs Abraham, Isaac and Jacob (aka Israel) had come from.

A further example, equally dramatic, was when the nation of Judah (what remained of Israel at that time) was carried into exile by the Babylonian Empire. Then, after the Persian Empire defeated the Babylonians, Jewish exiles were allowed to return to the land of Israel.