Isaac loved Esau because he ate of his game, but Rebekah loved Jacob.
28. 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.
We have here an account of the birth of Jacob and Esau, the twin sons of Isaac and Rebekah: their entrance into the world was (which is not usual) one of the most considerable parts of their story; nor is much related concerning Isaac but what had reference to his father while he lived and to his sons afterwards.
Commenting on Genesis 25:19-28
And Isaac loved Esau, because he did eat of his venison,.... Better than Jacob, not only because he was his firstborn, but because he brought him of the flesh of creatures, which he took in hunting, and being dressed, were savoury food to him: it is in the original, "because venison (or what he hunted) was in his mouth" (h), into which he put it...