John Calvin Commentary Genesis 27:37

"And Isaac answered and said unto Esau, Behold, I have made him thy lord, and all his brethren have I given to him for servants. And with grain and new wine have I sustained him. And what then shall I do for thee, my son?" — Genesis 27:37 (ASV)

Behold, I have made him your Lord. Isaac now more openly confirms what I have said before: that since God was the author of the blessing, it could be neither vain nor fleeting. For he does not magnificently boast of his dignity here, but keeps himself within the bounds and measure of a servant, and denies that he is free to alter anything.

For he always considers (and this is true) that when he acts as God's representative, he is not permitted to go further than the command allows.

Therefore, Esau should have learned from where he had fallen by his own fault, so that he might have humbled himself. He should have joined his brother to share in his blessing, as his inferior, rather than desiring anything separately for himself.

But a depraved greed carries him away, so that, forgetting the kingdom of God, he pursues and cares for nothing except his own private advantage.

Again, we must notice Isaac’s manner of speaking, by which he claims a certain force and effectiveness for his blessing, as if his word carried with it dominion, an abundance of grain and wine, and whatever else God had promised to Abraham.

For God, while requiring the faithful to depend on him alone, nevertheless would have them rest securely on the word, which, at his command, is declared to them by men. In this way, they are said to remit sins, who are only the messengers and interpreters of free forgiveness.