'These are the generations of Terah' means the origins and derivatives of the idolatry, from which a representative Church emerged. Terah was the son of Nahor, and also a nation that was named after him as its forefather. He means idolatrous worship. Abram, Nahor, and Haran were the sons of Terah and also nations that were named after them as their forefathers. Here they mean forms of idolatrous worship stemming from them. From Lot also two nations descended which were idolaters.