John Calvin Commentary Genesis 22:12

"And he said, Lay not thy hand upon the lad, neither do thou anything unto him. For now I know that thou fearest God, seeing thou hast not withheld thy son, thine only son, from me." — Genesis 22:12 (ASV)

Now I know that thou fearest God. The interpretation by Augustine, ‘I have caused you to know,’ is forced. But how can anything become known to God, to whom all things have always been present? Truly, by condescending to human ways of understanding, God here says that what He has demonstrated through this trial is now made known to Himself.

And He speaks this way to us, not according to His own infinite wisdom, but according to our weakness. Moses, however, simply means that Abraham, by this very act, testified how reverently he feared God.

However, it is asked whether Abraham had not already, on former occasions, given many proofs of his piety. I answer that when God had willed him to proceed this far, he had finally completed his true trial; for other people, a much lighter trial might have been sufficient.

And just as Abraham showed that he feared God by not sparing his own and only-begotten son, so a common testimony of the same fear is required from all the devout in acts of self-denial. Now, since God requires of us continual warfare, we must take care that no one desires release from it before the appointed time.