The LORD said to him, "Your descendants will be strangers in a foreign land; they will be slaves there and will be treated cruelly for four hundred years.

It will be four generations before your descendants come back here, because I will not drive out the Amorites until they become so wicked that they must be punished."

The Israelites had lived in Egypt for 430 years.

On the day the 430 years ended, all the tribes of the LORD's people left Egypt.

What I mean is that God made a covenant with Abraham and promised to keep it. The Law, which was given four hundred and thirty years later, cannot break that covenant and cancel God's promise.