John Calvin Commentary Genesis 25:27

"And the boys grew. And Esau was a skilful hunter, a man of the field. And Jacob was a quiet man, dwelling in tents." — Genesis 25:27 (ASV)

And the boys grew. Moses now briefly describes the dispositions of them both. He does not, indeed, commend Jacob because of those rare and excellent qualities, which are especially worthy of praise and of remembrance, but only says that he was simple. The word תם (tam), although generally understood as upright and sincere, is here used antithetically.

After the sacred writer has stated that Esau was robust and addicted to hunting, he contrasts this with the mild disposition of Jacob, who loved the quiet of home so much that he might appear indolent; just as the Greeks call those persons οἰκόσιτους oikositous, who, dwelling at home, show no sign of their industry.

In short, the comparison implies that Moses praises Esau for his vigor, but speaks of Jacob as being addicted to domestic leisure; and that he describes the disposition of the former as showing promise that he would be a courageous man, while the disposition of the latter had nothing worthy of commendation.

Since, by a decree of heaven, the honor of primogeniture would be transferred to Jacob, why did God allow him to lie down in his tent and to slumber among ashes; unless it is that He sometimes intends His election to be concealed for a time, so that people would not attribute something to their own preparatory actions?