When Abraham left Ur Kasdim and the idol-shops of his father Terach, he did not simply walk away. He pitched a tent, and the tent became a doorway.
The rabbis imagined the scene this way. Neighbors who already sensed that wood and stone could not answer prayer began drifting toward Abraham's camp. He was the ohev Hashem, the friend of God, and his reputation preceded him. Men gathered at his fire to learn, or simply to watch how a person could live without idols and still be whole.
The Book of Jasher (26:36) says plainly that Abraham brought all the children of the land to the service of God, and he taught them the ways of the Lord. The Targum Yerushalmi on Genesis 21 adds that Abraham's guests did not depart until he had made them proselytes. And his son Isaac, according to Targum Yonatan ben Uzziel, went to study at the Beit Midrash of Shem — the surviving son of Noah, who still remembered the world before the Flood.
The chain is unbroken. From Noah's ark to Shem's academy to Abraham's tent to Isaac's schoolroom — Judaism begins not as a religion of warriors or priests, but as a tradition of teachers who refused to let the old idols win.