John Calvin Commentary Genesis 25:28

"Now Isaac loved Esau, because he did eat of his venison. And Rebekah loved Jacob." — Genesis 25:28 (ASV)

And Isaac loved Esau. That God might more clearly show his own election to be sufficiently firm, to need no assistance elsewhere, and even powerful enough to overcome any obstacle whatever, he permitted Esau to be so preferred to his brother, in the affection and good opinion of his father, that Jacob appeared in the light of a rejected person.

Therefore, since Moses clearly demonstrates by so many circumstances that the adoption of Jacob was founded on the sole good pleasure of God, it is an intolerable presumption to suppose it depends on the will of man, or to ascribe it, in part, to means (as they are called) and to human preparations. But how was it possible for the father, who was not ignorant of the oracle, to be thus predisposed in favor of the firstborn, whom he knew to be divinely rejected?

Rather, it would have been the part of piety and modesty to subdue his own private affection, so that he might yield obedience to God. The firstborn holds a natural claim to the chief place in the parent’s affection; but the father was not at liberty to exalt him above his brother, who had been placed in subjection by the oracle of God.

What Moses adds is also even more shameful and unworthy of the holy patriarch: namely, that he had been induced to give this preference to Esau by the taste of his venison. Was he so enslaved to the indulgence of the palate that, forgetting the oracle, he despised the grace of God in Jacob, while he preposterously set his affection on him whom God had rejected?

Let the Jews now go and glory in the flesh, since Isaac, preferring food to the inheritance destined for his son, would pervert (as far as he had the power) the gratuitous covenant of God! For there is no room here for excuse, since with a blind, or, at least, a most inconsiderate love for his firstborn, he undervalued the younger.

It is uncertain whether the mother was chargeable with a fault of the opposite kind. For we commonly find the affections of parents so divided that if the wife sees any one of the sons preferred by her husband, she inclines, by a contrary spirit of emulation, more towards another.

Rebekah loved her son Jacob more than Esau. If, in so doing, she was obeying the oracle, she acted rightly; but it is possible that her love was ill-regulated. And on this point, the corruption of nature reveals itself only too well. There is no bond of mutual concord more sacred than that of marriage: children form still further links of connection, and yet they often prove to be the cause of dissension.

But since we soon afterward see Rebekah primarily concerned with the blessing of God, it is probable that she had been induced by divine authority to prefer the younger to the firstborn. Meanwhile, the father's foolish affection only illustrates more fully the grace of the divine adoption.