John Calvin on Genesis 28:15

15. I am with thee, and will keep thee. God now promptly anticipates the temptation which might steal over the mind of holy Jacob; for though he is, for a time, thrust out into a foreign land, God declares that he will be his keeper until he shall have brought him back again. He then extends his promise still further; saying, that he will never desert him till all things are fulfilled. There was a twofold use of this promise: first, it retained his mind in the faith of the divine covenant; and, secondly, it taught him that it could not be well with him unless he were a partaker of the promised inheritance.