GENESIS CHAPTER 22
"[The Angel of the Lord said to Abraham] 'Do not lay a hand on the boy,' He said. 'Do not do anything to him. Now I know that you fear God, because you have not withheld from Me your son, your only son."
Objectors falsely maintain that Abraham was not saved until this moment when he proved out his salvation by his obedience to God's command to go ahead and sacrifice Isaac.
However, this verse cannot say that God discovers by knowledge/experience in finite time that Abraham fears Him as a result of Abraham's faithful actions with Isaac. For that would make God less than One Who is omniscient Who does not have to wait upon man to do things so that He can discover whether man will go to heaven, fear Him, etc. The Bible teaches that God decrees all things and has done so before the creation of the universe  - so certainly He need not wait until Abraham is faithful in deeds in order to 'know' that Abraham fears God.
[Compare Ps 139:1-4, 16]:
(v. 1) "O LORD, you have searched me and you know me.
(v. 2) You know when I sit and when I rise; You perceive my thoughts from afar.
(v. 3) You discern my going out and my lying down; You are familiar with all my ways.
(v. 4) Before a word is on my tongue you know it completely, O LORD.
(v. 16) Your eyes saw my unformed body. All the days ordained or me were written in Your book before one of them came to be."
Incidentally, Abraham had already demonstrated faithfulness when he left Ur and demonstrated repeatedly his trust in God's promise of a son through Sarah.
Furthermore, fearing God is not the same thing as being justified unto eternal life. So the objector is comparing apples and oranges in his insistance that this is a soteriological statement. Indeed, the demons have often demonstrated actions one might render as fearing God. Are they saved as a result?
Finally, the language of Gen 22:12 certainly allows one to interpret this passage as follows:
The Angel of the Lord is saying to Abraham 'by your faithful actions I know, i.e., observe, that you fear God.' This then would not violate God's omniscience and convey the message to Abraham and all who read this passage that by ones works one demonstrates what one believes to those who observe ones actions - in this case the Angel of the Lord. Thus what is being stated serves to commend Abraham for his faithful actions. It cannot serve notice to Abraham that he is finally saved as a result of his actions since salvation by grace through faith, not of oneself, it is a gift and not of works, so that no one can boast, (Eph 2:8-9). If super extraordinarily faithful works such as Abraham did when he took steps to sacrifice his one and only son of the promise,Isaac, were necessary, most believers would not make it to heaven - it would be an empty place.
[John W. Haley states, "Alleged Discrepancies of the Bible", Whitaker House, New Kensington, Pa, 1992., pp. 56-57]:
"[Re: Gen 22:12] The language is accommodated to the human understanding, uttered, as it were, from man's point of view. By the testing process applied to Abraham and the Israelites, the knowledge which had hidden in the divine mind was revealed and verified.
The words addressed to Abraham, 'Now I know that,' etc., are equivalent to saying, Now I have established by actual experiment that which I previously knew. I have demonstrated, made manifest by evident proof, my knowledge of thy character...
The language in Genesis may be illustrated as follows: A chemical professor, lecturing to his class, says: 'Now I will apply an acid to this substance, and see what the result will be.' He speaks in this way, although he knows perfectly well beforehand. Having performed the experiment, he says, 'I now know that such and such results will follow.' In saying this he puts himself in the place of the class, and speaks from their stand-point."
So did the Angel of the Lord declare Abraham righeous right then and there unto eternal life when Abraham proved himself faithful? No! That would contradict Scripture and impugn the integrity of God. For God declared Abraham rightous in Gen 15:6 on the basis of Abraham's faith alone in God's plan of eternal life for him long before Isaac was born. Would a Holy and Righteous God then add another condition of receiving justification by requiring Abraham to do something when He had already declared Abraham justified long before Isaac just so that He could redeclare Abraham justified but this time under the new conditions having reneged on His promise years before that by a moment of faith alone?
Finally, just as a human father can commend his son for extraordinary actions honoring the father by saying, "Son, now I know you truly are my son" all the while the father of course knowing beforehand who his son is, so much the more can God commend Abraham as one who fears Him as a result of Abraham's extraordinarily faithful actions by saying, "Now I know that you fear God, because you have not withheld from Me your son, your only son" yet can God know already that Abraham feared Him 38 years before that when Abraham trusted in His plan of salvation through Abraham's seed, (Gen 15:6).