@dad,
You are right, God told Abraham in Genesis 15:16 that his descendants will return to the land of Canaan in their own strength. Here is the passage which contains three separate prophecies,
1. Concerning the nation of Israel becoming slaves in Egypt and that God will bring them out with great possessions and that he will also judge that nation for their deeds against the nation of Israel while they lived in Israel.
2. Concerning Abraham that he would live out his days in peace and be buried at a good age.
3. That some of Abraham's descendants will return to the Land of Canaan in the fourth age of their existence in their own strength seeking God, but God will not give them any assistance like He said he would when He brought out of Egypt. We are also told in this one verse prophecy that the iniquities of the Amorite people would not be compete when they return.
Genesis 15:12-16: - 12 Now when the sun was going down, a deep sleep fell upon Abram; and behold, horror and great darkness fell upon him. 13 Then He said to Abram: "Know certainly that your descendants will be strangers in a land that is not theirs, and will serve them, and they will afflict them four hundred years. 14 And also the nation whom they serve I will judge; afterward they shall come out with great possessions. 15 Now as for you, you shall go to your fathers in peace; you shall be buried at a good old age. 16 But in the fourth generation/age they shall return here, for the iniquity of the Amorites is not yet complete."
From my research, I ascertained that Isaac was born at the beginning of the year 2052 BC and that some of Abraham's descendants returned in the year 1948 AD, 4,000 years after the birth of Isaac, Abraham's first descendant that fulfilled God's promises to Abraham.
Shalom.
PS: - In the prophecies in Ezekiel where God has said that He will Gather Israel to Himself, His word is that he will plant them in the fertile field of "Israel," i.e. Christ, and teach them on, i.e. about, the mountain, i.e. religion, of "Israel," i.e. Christ, where they are living in the valleys and ravines beside the rivers where they have been scattered through the whole earth. We really need to be careful that we do not confuse what the translators have wrtten in their translations which do not reflect the same contextual messages as contain in the Hebrew texts in which they were contained.