God foreknew what Abraham would do, so why would God say "
NOW I know" AFTER Abraham obeyed?
Could it be that God was using some "accomodative language" in helping Abraham to understand that by his act of obedience that God NOW knows he feared God as proven by his actual obedience? Yes. So this is why James would say "
by works a man is justified"
"Now I know…
This, along with James' declaration that Abraham was justified when he offered up Isaac makes mandatory the conclusion that God's final approval of Abraham as the instrument of his purpose occurred right here. The truth that God already knows everything does not nullify this. The great corollary for all people is simply this: God tests every person who would receive eternal life. If God compelled Abraham to withstand such a (obedient) test as this, how could it ever be imagined that God today saves people merely upon the glib assertion of their faith (only)? The test for all people now was announced by Christ himself: He that believeth and is baptized shall be saved (Mark 16:16)."
Coffman Commentary (my emp)
So when one believes and is baptized Christ "now knows" that person fears Him seeing that person has obeyed His words (pass the test as Abraham).