John Calvin Commentary Genesis 13:14

"And Jehovah said unto Abram, after that Lot was separated from him, Lift up now thine eyes, and look from the place where thou art, northward and southward and eastward and westward:" — Genesis 13:14 (ASV)

And the Lord said to Abram. Moses now relates that after Abram was separated from his nephew, divine consolation was given to appease his mind. There is no doubt that the wound inflicted by that separation was very severe, since he was obliged to send away one who was as dear to him as his own life. Therefore, when it is said that the Lord spoke, the circumstance of time should be noted, as if he had said that the medicine of God’s word was now brought to alleviate his pain. And so he teaches us that the best remedy for lessening and curing sadness is found in the word of God.

Lift up now your eyes. Since the Lord promises the land to Abram's seed, we perceive God's admirable design in Lot's departure. He had assigned the land to Abram alone; if Lot had remained with him, the children of both would have been mixed together.

The cause of their dissension was indeed culpable; but the Lord, according to his infinite wisdom, turns it to a good outcome, so that Lot's posterity would possess no part of the inheritance. This is the reason why he says, All the land which is before you, I assign to you and to your seed. Therefore, there is no reason why you, to whom such an excellent reward is to be given hereafter, should be excessively sorrowful and troubled on account of this solitude and privation.

For although the same thing had already been promised to Abram, God now adapts his promise to relieve the present sorrow.

And so it should be remembered that not only was a promise repeated here that could cherish and confirm Abram’s faith, but also that a special oracle was given from which Abram could learn that the interests of his own seed were to be promoted by Lot's separation from him.

Luther's speculation here (as in other places) has no solidity; namely, that God spoke through some prophet. In promising the land for ever, he does not simply denote perpetuity, but rather that period which was brought to a close by the advent of Christ.

Concerning the meaning of the word עולם (olam), the Jews ignorantly contend. But since it is used in various senses in Scripture, it comprises in this place (as I have recently hinted) the whole period of the Law, just as the covenant that the Lord made with his ancient people is, in many places, called eternal, because it was Christ's office by his coming to renovate the world.

But the change that Christ introduced was not the abolition of the old promises, but rather their confirmation. Therefore, since God does not now have one peculiar people in the land of Canaan, but a people diffused throughout all regions of the earth, this does not contradict the assertion that the eternal possession of the land was rightly promised to Abram's seed until the future renovation.