John Calvin Commentary Genesis 27:21

"And Isaac said unto Jacob, Come near, I pray thee, that I may feel thee, my son, whether thou be my very son Esau or not." — Genesis 27:21 (ASV)

Come near, I pray thee, that I may feel thee. From this it appears that the holy man was suspicious of fraud and therefore hesitated. For this reason, it may seem that the blessing was vain, since it had no support of faith. But it pleased God in this way to perform His work by the hand of Isaac, so as not to make him, who was the instrument, a willing promoter of His design.

Nor is it absurd that Isaac, like a blind man, would ignorantly transfer the blessing to a different person from the one he intended. The ordinary function of pastors is somewhat similar; for since, by God's command, they reconcile people to Him, yet they do not discern to whom this reconciliation comes. Thus they scatter the seed but are uncertain about the fruit.

Therefore, God does not place the office and power with which He has invested them under the control of their own judgment. In this way, Isaac's ignorance does not nullify the heavenly oracles; and God Himself, although His servant's senses fail, does not cease from accomplishing His purpose.

Here we have a clear refutation of the figment of the Papists, that the whole force of the sacrament depends upon the intention of the man who consecrates, as if, indeed, it were left to human will to frustrate God's design. Nevertheless, what I have already said so often must be remembered: however Isaac might have been deceived about his son's identity, he still did not pronounce the blessing in vain, because a general faith remained in his mind and partly governed his conduct.

In forming his judgment from touch, disregarding the voice, he did not act according to the nature of faith. And therefore, concerning the person, he was plainly in error. This, however, did not happen as a consequence of negligence, since he diligently and even anxiously considered every aspect, so that he might not deprive the firstborn of his right.

But it pleased the Lord in this way to dull his senses, partly to show how vain it is for people to strive to change what He has once decreed (because His counsel must inevitably remain firm and stable, even if the whole world opposes it), and partly to correct, by this kind of chastisement, the absurd attachment by which Isaac was too closely bound to his firstborn.

For what caused this minute investigation, except that an inordinate love for Esau, which had taken complete possession of his mind, turned him away from the divine oracle? Therefore, since he yielded an excessive indulgence to natural feeling, he deserved in every way to be blinded. We ought to take so much greater care that, in carrying on God’s work, we do not give free rein to our human affections.