12. How did Judaism evolve away from its polytheistic roots into a monotheistic religion?

The evolution of Judaism’s polytheistic roots to a monotheistic religion was a slow progression and did not happen overnight. In fact, just like the Hebrew history, the development was a long and rocky road. Major shifts inspired major changes in the religion itself and it wasn't really until after the Exilic revolution that the Torah was completed.
During Judaism’s “Pre-Mosaic stage,” polytheism and animistic practices were common. In fact, as mentioned in Genesis chapter 11, Abraham worshipped Elohim, which is translated into “more than one God.” It is believed that the introduction of Yahweh worship and monotary occurred during the migration from Egypt.
After the migration, Judaism adopted a single, local god as their god. Then came the “Prophetic Revolution,” in which the religion grew under the intellectual leadership of a few "prophets" or "prophetic" writers. “Mosaic Judaism,” or Judaism brought by Moses, taught henotheism (the belief in one God that is superior to all other gods) was under this umbrella as well. Moses introduced Yahweh as the God above all other gods, or the only god deserving worship.
The disaster of the Exile led to the rethinking of the Yahweh religion and the elevation of the Torah as the single, unsullied law for the Hebrews, and by the time the Hebrews were established in Jerusalem, Yahweh had become the only God, thus the origin of monotheism.