God knew the sincerity and resolvedness of Abraham's faith and obedience before and without this evidence, and from eternity foresaw this fact and all its circumstances; and therefore you must not think that God had now made any new discovery: but this is spoken here, as in many other places, of God after the manner of men, who is then said to know a thing, when it is notorious and evident to a man's self and others by some remarkable effect. Thus David prayed that God would search and know his heart, and his thoughts, Psalms 139:23, though he had before professed that God understood his thought afar off, Genesis 22:2. This therefore is the sense: Now I know, i.e. Now I have what I designed and desired; now I have made thee and others to know. As the Spirit of God and of Christ is said to cry Abba, Father, Galatians 4:6, when it makes us to cry so, Romans 8:15. Thou hast not withheld thy son from me, for my service and sacrifice; or for me, i.e. for my sake; i.e. thou hast preferred mine authority and honour before the life of thy dear son. By which words it appears that God himself speaks these words.
Related Commentaries of Genesis 22:12
Genesis 22:12
12 And he said, Lay not thine hand upon the lad, neither do thou any thing unto him: for now I know that thou fearest God, seeing thou hast not withheld thy son, thine only son from me.