In Genesis 15:13, the Lord tells Abraham, “Know for certain that your offspring will be sojourners in a land that is not theirs and will be servants there, and they will be afflicted for four hundred years.” God knows everything that will happen, and He revealed part of the future to Abraham. God’s plan included sending the Jews to Egypt for four hundred years.
As for why, some information is provided in the context of this verse. Verses 14-16 read, “But I will bring judgment on the nation that they serve, and afterward they shall come out with great possessions. . . . And they shall come back here in the fourth generation, for the iniquity of the Amorites is not yet complete.” Two major predictions help explain this 400-year waiting period.
First, one result of the Israelites’ leaving Egypt would be “great possessions.” Of course, in order to leave Egypt, they had to be there. God promised that their exit would mean great abundance for Israel. This was fulfilled in Exodus 12. When the Israelites left Egypt following the tenth plague, they were told to ask the Egyptians for items of value for their journey. “The people of Israel . . . asked the Egyptians for silver and gold jewelry and for clothing. And the LORD had given the people favor in the sight of the Egyptians, so that they let them have what they asked. Thus they plundered the Egyptians” (verses 35-36).
Second, the Lord wanted to wait before giving the Promised Land to Israel because “the iniquity of the Amorites is not yet complete.” The Amorites worshiped other gods and participated in numerous other sins. God promised to remove them from the land where Israel would one day live. However, God had a certain time period in mind that included 400 years for Israel in Egypt. He is surely “slow to anger, and abounding in mercy” (Psalm 103:8). Once the Israelites did return to the land promised to them, the Amorites were destroyed as the Lord predicted (Numbers 21:31-32; Joshua 10:10; 11:8).
God certainly could have chosen a different way or a different time frame for placing the Israelites in their Promised Land, but He chose a particular way to bring glory to Himself. The 400-year sojourn in Egypt included many examples of God’s wisdom and might. Joseph’s preservation of the Israelites during a famine, Moses’ rise to leadership, and God’s great miracles such as the crossing of the Red Sea were all part of Israel’s time in Egypt.