Why did Abraham found Judaism?
The Bible attributes no reason to Abraham for founding Judaism. Nowhere in the story of Abraham (Genesis 11:26-25:8) is there any suggestion that Abraham even founded Judaism, and Genesis does not even credit Abraham with monotheistic beliefs. Certainly, Genesis speaks of God talking to Abraham, and testing him, but there is no suggestion that Abraham felt compelled to describe these experiences to anyone else or to proselytise a monotheistic religion. And there is nothing in any of the following chapters of Genesis to suggest that a new religion had been founded by Abraham. No reason is attributed to Abraham for founding Judaism, and no evidence provided that he did do so.