Why did Abraham's descendants have to stay out of the land of Canaan for 400 years?
Abraham's descendants had to remain outside Canaan for 400 years because the iniquity of the Canaanites was not yet full. God was giving the Canaanite people that period to straighten up their act, but they instead went deeper into wickedness, so judgment later fell when Joshua led Israel across the Jordan.
Les explains that in the Abrahamic Covenant God told Abraham his offspring would end up in a land that was not theirs and would be there in slavery for 400 years. The reason the children of Abraham had to stay out of the land of Canaan was that the iniquity of the Canaanites was not yet full. In other words, God gave the Canaanite people 400 years to straighten up their act, but instead they went deeper and deeper into wickedness. So finally, when Joshua came across the Jordan River, God told Joshua and the children of Israel to destroy the Canaanites and not spare a single one, because they had gone down so far. Les also sees the Gentile world fast approaching the same place.