John Calvin Commentary Genesis 27:1

"And it came to pass, that when Isaac was old, and his eyes were dim, so that he could not see, he called Esau his elder son, and said unto him, My son. And he said unto him, Here am I." — Genesis 27:1 (ASV)

And it came to pass that when Isaac was old. In this chapter Moses details, at length, a history that does not appear to be of great utility. It amounts to this: Esau having gone out, at his father’s command, to hunt, Jacob, in his brother’s clothing, was, by the artifice of his mother, induced to obtain by stealth the blessing due by natural right to the firstborn.

It seems even like child’s play to present to his father a kid instead of venison, to feign being hairy by putting on skins, and, under his brother's name, to get the blessing by a lie. But in order to learn that Moses does not pause over this narrative in vain as a very serious matter, we must first observe that when Jacob received the blessing from his father, this token confirmed to him the oracle by which the Lord had preferred him to his brother.

For the blessing spoken of here was not a mere prayer but a legitimate sanction, divinely ordained, to reveal the grace of election. God had promised to the holy fathers that he would be a God to their seed forever. They, when at the point of death, so that the succession might be secured for their posterity, put them in possession, as if they were delivering, from hand to hand, the favor they had received from God.

So Abraham, in blessing his son Isaac, constituted him the heir of spiritual life with a solemn rite. With the same intention, Isaac now, being worn down with age, imagines he will soon depart this life, and wishes to bless his firstborn son, so that the everlasting covenant of God may remain in his family.

The Patriarchs did not undertake this rashly, or on their own private initiative, but were public and divinely ordained witnesses. Relevant to this is the Apostle's declaration, the less is blessed of the better (Hebrews 7:7). For even the faithful were accustomed to bless each other through mutual acts of love; but the Lord entrusted this special duty to the patriarchs, that they should transmit to posterity, as a deposit, the covenant he had made with them, and which they kept throughout their lives.

The same command was later given to the priests, as appears in Numbers 6:24 and other similar passages. Therefore Isaac, in blessing his son, acted in a different capacity than that of a father or a private individual, for he was a prophet and an interpreter of God, appointing his son an heir of the same grace he himself had received.

This makes clear what I have already said: that Moses, in discussing this matter, is not lengthy without reason. But let us consider each circumstance of the case in its proper order; the first of which is that God transferred Esau's blessing to Jacob through a mistake on the father's part, whose eyes, Moses tells us, were dim.

Jacob's vision was also poor when he blessed his grandchildren Ephraim and Manasseh; yet his lack of sight did not prevent him from carefully placing his hands crosswise. But God allowed Isaac to be deceived to show that Jacob was raised to the right and honor of primogeniture, contrary to the course of nature, not by human will.