Acts 7:17-18

Stephen had gotten ahead of himself briefly in Acts 7:16. Now he returned to his history of Israel just before the Exodus. "The promise" God had made to Abraham was that He would judge his descendants’ enslaving nation and free the Israelites (Genesis 15:14). This was a particular way that He would fulfill the earlier promises to give Israel the land, to multiply the Israelites, and to curse those nations that cursed Israel (Genesis 12:1-3; Genesis 12:7). The Israelites increased in Egypt until another Pharaoh arose who disregarded Joseph (Exodus 1:7-8).

Similarly Christ had come in the fullness of time (Galatians 4:4). Before Moses appeared on the scene, Israel increased in numbers and fell under the control of an enemy that was hostile to her. Likewise before Jesus appeared, Israel had increased numerically and had fallen under Roman domination.