I agree, if you remove the word "eventually". He was justified in Gen. 15.
Rom. 4:13 doesn't say
promises, it says promise, singular. The promise he is talking about is the promise that Abraham would be "heir of the world", which was first made in Gen. 12.
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and the father of circumcision to those who not only are of the circumcision, but who also follow in the steps of the faith of our father Abraham which he had while uncircumcised. For the promise to Abraham or to his descendants that he would be heir of the world was not through the Law, but through the righteousness of faith." (Rom 4:12-13 NASB)
As you said, Paul is chronicling the faith of Abraham here and it starts in Gen. 12, when he first had faith (Heb. 11). Did this faith justify him? Paul plainly says that this faithful acceptance was "through the righteousness of faith". So the answer is clearly "yes". Even if we ignore the overwhelming evidence I laid out on Heb. 11 (which you have been doing), this alone should be enough to prove that in Paul's mind, Abraham accepted the "promise" in Gen. 12 "through the righteousness of faith", and this plainly means he was justified.
Well, actually there is a lot if inference packed in that sentence.
More inference. Rom. 4 doesn't say "Abraham never wavered in his faith", it says:
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yet, with respect to the promise of God, he did not waver in unbelief but grew strong in faith, giving glory to God," (Rom 4:20 NASB).
This is one, specific aspect of faith he is talking about here. He is saying that Abraham never doubted the "promise of God", not "never doubted God". Abraham had faith "that what God had promised, He was able also to perform". (v.21). That doesn't translate into "never wavered in his faith". He could have "wavered" when it came to other aspects not related to "the promise". Also, when did this "not wavering" and "growing strong in faith" start? It seems from the text like it started in Gen. 17, since this is the part of the chronology that it appears in.
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(as it is written, "A FATHER OF MANY NATIONS HAVE I MADE YOU") in the presence of Him whom he believed, even God, who gives life to the dead and calls into being that which does not exist. In hope against hope he believed, so that he might become a father of many nations according to that which had been spoken, "SO SHALL YOUR DESCENDANTS BE." Without becoming weak in faith he contemplated his own body, now as good as dead since he was about a hundred years old, and the deadness of Sarah's womb; yet, with respect to the promise of God, he did not waver in unbelief but grew strong in faith, giving glory to God, and being fully assured that what God had promised, He was able also to perform." (Rom 4:17-21 NASB)
Since he says "yet" here, he is tying the "not wavering" to what came before, namely the faith Abraham showed by trusting God and not doubting that God could bring forth a son from two very old people, which he had misunderstood before that. Remember, he thought "the promise" was coming through Ishmael (Gen. 13). He still believed the promise from Gen. 12 that he would be "heir of the world", but now he believed it even though it seemed impossible. Now he "grew strong in faith" because he believed that God could bring forth a son from "the deadness of Sarah's womb", which was impossible in his mind.
While we're on the subject, I don't ever remember insinuating that "doubt" was the only thing that would remove justification from a person. I know I said that I thought Abraham "doubted" in Gen. 17 when he "laughed", but you and
StoveBolts showed me I was in error. I have been, for the sake of argument here, purposely not engaging in
what justifies, so I might have implied that this is what I believe. I do believe that doubt (lack of faith) certainly will "unjustify" a person, but that's not even close to the only reason that people need to repent and return to Christ. We are justified by
obedient faith, just like you believe about salvation. When either "obedience" or "faith" is lacking, repentance is necessary to justify the sinner. We are not justified by obedience alone, without faith. We are not justified by faith alone without obedience. Lack of either of these, requires "rejustification".