Then the LORD said to Abram, “Know for certain that your descendants will be strangers in a land that is not their own, and they will be enslaved and mistreated four hundred years.
We have here a full and particular discovery made to Abram of God's purposes concerning his seed. Observe, I. The time when God came to him with this discovery: When the sun was going down, or declining, about the time of the evening oblation, Kg1 18:36; Dan 9:21.
Commenting on Genesis 15:12-16
And also that nation whom they shall serve will I judge,.... It is not said "the land" in which they were strangers, though God did judge, condemn, and punish the inhabitants of the land of Canaan, and drove them out of it, to make way for Israel; but the "nation" they should "serve", meaning the Egyptians, to whom they became servants, and were very hardly...
And he said unto Abram, Know of a surety that thy seed shall be a stranger in a land [that is] not theirs, and shall serve them; and they shall afflict them four hundred years; (d) Counting from the birth of Isaac to their departure of Egypt: Which declares that God will allow his to be afflicted in this world.