Why did Israel have to go into Egypt and slavery before coming out under Moses?
Israel had to go into Egypt and slavery because it was part of God's eternal divine purpose. There, God would multiply them into a great nation, more numerous than other Middle East peoples, and prepare them to come out under Moses some 215 years later. This aligned with their earthly promises, not heavenly.
Les teaches that Israel's Egyptian sojourn and slavery were not accidents but were part of God's eternal purposes. God was remembering His promise to Abraham that his offspring would be as numerous as the pebbles of sand, and He directed them down into Egypt where Joseph had food aplenty. There the Jews would have a population explosion, coming out some 215 years later as five, six, or seven million—more numerous than any other single tribe or nation in the Middle East. They had to go down into Egypt, had to go into slavery, and had to be ready to come out when Moses led them. Les emphasizes that this fit Israel's earthly promises, not heavenly ones; God never speaks of the nation of Israel going to heaven, but of an earthly kingdom with their Messiah as King.