John Calvin Commentary Genesis 28:15

"And, behold, I am with thee, and will keep thee, whithersoever thou goest, and will bring thee again into this land. For I will not leave thee, until I have done that which I have spoken to thee of." — Genesis 28:15 (ASV)

I am with thee, and will keep thee. God now promptly anticipates the temptation that might creep into the mind of holy Jacob; for though he is, for a time, driven out into a foreign land, God declares that he will be his protector until he has brought him back. He then extends his promise still further, saying that he will never desert him until all things are fulfilled. This promise had a twofold purpose: first, it maintained his faith in the divine covenant; and, secondly, it taught him that it could not go well for him unless he shared in the promised inheritance.