Why did the Israelites prosper and multiply in Egypt?
During the 430-year span foretold by God, with 215 years remaining after Jacob entered Egypt, the Israelites remained in Goshen. As long as Joseph was alive, things went well for them. Goshen was the best productive area, near the Nile, so they prospered and, prospering, multiplied.
Les explains that when the brethren sold Joseph into Egypt and all twelve sons ended up there through their sin, God lost control of His covenant people and would have to buy them back. Yet this was in His sovereign plan: Israel would become a nation while in Egypt. At this point Jacob had gone down into Egypt, in the middle of the 430-year time span God had foretold, with 215 years elapsed from Abraham's call and 215 years left. As long as Joseph was alive, things went well for the Israelites. They had it good in Goshen, the best productive area, right by the Nile River. They prospered, and as they prospered, they multiplied.