I agree that we know what justification is based upon, given the revelation of New testament. What I am asking is, what did Moses understand? Looking at that text, given it's historical setting, would it be justifiable to understand that the Jews, by and large, would understand justification by faith alone.
Revelation is
progressive and there are many things written in the OT that the writer could not understand at the time it was written.
1Peter 1:8 Whom having not seen, ye love; in whom, though now ye see
him not, yet believing, ye rejoice with joy unspeakable and full of glory:
1Peter 1:9 Receiving the end of your faith,
even the salvation of
your souls.
1Peter 1:10 Of which salvation the prophets have enquired and searched diligently, who prophesied of the grace
that should come unto you:
1Peter 1:11 Searching what, or what manner of time the Spirit of Christ which was in them did signify, when it testified beforehand the sufferings of Christ, and the glory that should follow.
1Peter 1:12 Unto whom it was revealed, that
not unto themselves, but
unto us they did minister the things, which are now reported unto you by them that have preached the gospel unto you with the Holy Ghost sent down from heaven; which things the angels desire to look into.
Psalms 2 was written by David but we now know that it refers to Jesus according to Acts 4:25 and is sometimes referred to as
“the law of subsequent narration.” This sheds light on a lot of the Psalms where the original writer may not have known all the details of the events he was describing but is revealed to us in the NT. In
Luke 24:27 Jesus after His resurrection expounded to the disciples scriptures concerning Himself that up to then had been a mystery as to exactly what the prophets were saying.
The David Jeremiah Study Bible has an article on how the OT saints were saved by faith and I think it sums everything up quite well:
“Many Jewish people at the time of Jesus believed that salvation was a “reward” for keeping the law of God. Orthodox Jews in our own day speak of works of righteousness such as public reading of Torah, reciting prayers, and giving to the poor as ways to placate God instead of offering sacrifices since there is no temple today. If the keeping of rules were a possible means of achieving salvation from sin and death, then Jesus’ sacrifice and resurrection – His atonement for our sins - would be unnecessary.
Many Jewish people in Paul’s day argued that a man had to be circumcised and he had to keep the law in its fullness to he saved (Acts 15:5). Paul, however shows in Romans 4 that Abraham was justified by his
faith, quoting Genesis 15:6 and
his acceptance of the rite of circumcision (17:26) was an act of obedience by a person who was already saved. Believing in God and acting on that belief as a demonstration of faith have always been the way to “get right” with God.
In the later periods of OT times, obedience to the laws God gave through Moses was no more a means of salvation than it is in NT times. However,
compliance with God’s laws was a witness to one’s faith in God. As Jesus said, ‘But why do you call Me Lord,” and not do the things which I say” (Luke 6:46).
True faith is always expressed by actions that please God.
Faith is the same for us as for Noah, Abraham, and anyone else who has ever believed: it is
“being sure of what we hope for and certain of what we do not see” (Heb 11:1). And
“without faith it is impossible to please [God], for he who comes to God must believe that He is, and that He is a rewarder of those who diligently seek Him” (Heb 11:6)."