Jacob’s family stayed in Egypt for a long time as part of God's plan. God told Abraham that his descendants would not receive the land of Canaan for 400 years, until the Canaanites' sins were complete (Genesis 15:13–16).
Even in Egypt, God's promises were working. The descendants of the elderly Abraham and barren Sarah multiplied … exceedingly, just as God had said (Genesis 15:5). This was because God blessed them (Psalm 105:24).