John Wesley on Genesis 15:14

That nation whom they shall serve, even the Egyptians, will I judge - This points at the plagues of Egypt, by which God not only constrained the Egyptians to release Israel, but punished them for all the hardships they had put upon them. The punishing of persecutors is the judging of them; it is a righteous thing with God, and a particular act of justice, to recompense tribulation to those that trouble his people. 3. The deliverance of Abram's seed out of Egypt. And afterwards shall they come out with great substance - Either after they have been afflicted 400 years, or, after the Egyptians are judged and plagued.