I see we are in agreement on the main points. You regard this as "being saved by Paul's Gospel".
For my case, its more straightforward, during the dispensation of the law, you exhibit faith by "obeying the law", all the Jews have to obey the law. It is true that all the saints of past ages were saved through the merits of Christ's shed blood, but not through their faith in that shed blood.
Those of past ages were expected to believe only what God had thus far revealed, or what He had revealed to them. In other words, they were saved simply because they trusted God and believed what He said. The full plan of salvation has since been unfolded, but the Scriptures make it crystal clear that these believers were saved without even understanding that Christ would die for them.
When God says, "Sacrifice an animal every time you sin," what will faith do? Just one thing: sacrifice an animal whenever you sin. We know, thanks to Hebrews, that such sacrifices are a mere shadow of the coming Jesus as the final Lamb, yet not one of their hearers would have interpreted this action to mean what it meant in Paul's Gospel: "Trust in the death of Christ for salvation."
But when God now says, thru the Apostle Paul, "BUT NOW the righteousness of God without the law is manifested" (Rom. 3:21); "To him that worketh not, but believeth on Him that justifieth the ungodly, his faith is counted for righteousness" (Rom. 4:5); "Being Justified freely by His grace, through the redemption that is in Christ Jesus" (Rom. 3:24); "In whom we have redemption through His blood, the forgiveness of sins according to the riches of His grace" (Eph. 1:7); "Not by works of righteousness which we have done, but according to His mercy He saved us" (Tit. 3:5); "Not of yourselves: it is the gift of God: not of works, lest any man should boast" (Eph. 2:8,9) -
When God now says this, what will faith do? Faith will say, "This is the most wonderful offer ever made by God to man. I cannot refuse it. I will trust Christ as my Savior and accept salvation as the free gift of God's grace."