From Volume 1 of Calvin’s Commentaries on Genesis:
12. Now I know that thou fearest God. The exposition of Augustine, ‘I have caused thee to know,’ is forced. But how can any thing become known to God, to whom all things have always been present? Truly, by condescending to the manner of men, God here says that what he has proved by experiment, is now made known to himself. And he speaks thus with us, not according to his own infinite wisdom, but according to our infirmity. Moses, however, simply means that Abraham, by this very act, testified how reverently he feared God. It is however asked, whether he had not already, on former occasions, given many proofs of his piety? I answer that when God had willed him to proceed thus far, he had, at length, completed his true trial; in other persons a much lighter trial might have been sufficient.449 And 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 pious, in acts of self-denial. Now since God enjoins upon us a continual warfare, we must take care that none desires his release before the time.