Isaac’s two sons, Esau and Jacob, grew up together. The primacy of the elder was transferred to the younger by a bargain and agreement between them, when the elder immoderately lusted after the lentils the younger had prepared for food, and for that price sold his birthright to him, confirming it with an oath. We learn from this that a person is to be blamed, not for the kind of food he eats, but for immoderate greed.
Isaac grew old, and old age deprived him of his eyesight. He wished to bless the elder son, and instead of the elder, who was hairy, unwittingly blessed the younger, who put himself under his father’s hands, having covered himself with kid-skins, as if bearing the sins of others. Lest we should think this guile of Jacob’s was fraudulent guile, instead of seeking in it the mystery of a great thing, the Scripture has predicted in the words just before, Esau was a cunning hunter, a man of the field; and Jacob was a simple man, dwelling at home. Genesis 25:27 Some of our writers have interpreted this, without guile. But whether the Greek ἄλαστος means without guile, or simple, or rather without reigning, in the receiving of that blessing what is the guile of the man without guile? What is the guile of the simple, what the fiction of the man who does not lie, but a profound mystery of the truth?
But what is the blessing itself? See, he says, the smell of my son is as the smell of a full field which the Lord has blessed: therefore God give you of the dew of heaven, and of the fruitfulness of the earth, and plenty of grain and wine: let nations serve you, and princes adore you: and be lord of your brethren, and let your father’s sons adore you: cursed be he that curses you, and blessed be he that blesses you. Genesis 27:27-29 The blessing of Jacob is therefore a proclamation of Christ to all nations.
It is this which has come to pass, and is now being fulfilled. Isaac is the law and the prophecy: even by the mouth of the Jews Christ is blessed by prophecy as by one who knows not, because it is itself not understood. The world like a field is filled with the odor of Christ’s name: His is the blessing of the dew of heaven, that is, of the showers of divine words; and of the fruitfulness of the earth, that is, of the gathering together of the peoples: His is the plenty of grain and wine, that is, the multitude that gathers bread and wine in the sacrament of His body and blood. Him the nations serve, Him princes adore. He is the Lord of His brethren, because His people rules over the Jews. Him His Father’s sons adore, that is, the sons of Abraham according to faith; for He Himself is the son of Abraham according to the flesh. He is cursed that curses Him, and he that blesses Him is blessed.
Christ, I say, who is ours is blessed, that is, truly spoken of out of the mouths of the Jews, when, although erring, they yet sing the law and the prophets, and think they are blessing another for whom they erringly hope. So, when the elder son claims the promised blessing, Isaac is greatly afraid, and wonders when he knows that he has blessed one instead of the other, and demands who he is; yet he does not complain that he has been deceived, yea, when the great mystery is revealed to him, in his secret heart he at once eschews anger, and confirms the blessing. Who then, he says, has hunted me venison, and brought it me, and I have eaten of all before you came, and have blessed him, and he shall be blessed? Genesis 27:33 Who would not rather have expected the curse of an angry man here, if these things had been done in an earthly manner, and not by inspiration from above? O things done, yet done prophetically; on the earth, yet celestially; by men, yet divinely! If everything that is fertile of so great mysteries should be examined carefully, many volumes would be filled; but the moderate compass fixed for this work compels us to hasten to other things.
[Augustine of Hippo, City of God, Book 16]