I agree with you, salvation is always by grace thru faith alone, since Adam. But you need to understand the concept of progressive revelation.
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, "Repent and be baptized for the remission. of sins," what will faith do? Just one thing: repent and be baptized. We know that oceans of water cannot wash away one sin, yet when John the Baptist and Peter preached repentance and baptism for remission not one of their hearers would have interpreted their words to mean: "Trust in the death of Christ for salvation."
Indeed, when God required water baptism for salvation the only way to manifest faith was to be baptized, and those who refused to do so were condemned for their unbelief:
"But the Pharisees and lawyers REJECTED THE COUNSEL OF GOD AGAINST THEMSELVES, BEING NOT BAPTIZIED OF HIM" (Luke 7:30).
But under the Gospel of Grace, let the Apostle Paul, our Apostle, spell out the church doctrine for salvation now.
"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."
Trust me when I tell you, everyone else from the Old Testament, King David, Noah, even the 4 Gospels guys such as Peter, James and John, will be very envious about you.
Their conditions for showing faith were not as simple as what we have to do, under the age of Grace.
Noah had to build an ark. (Hebrews 11:7)
Abel had to bring the correct sacrifice (Gen 4:4-5, Heb. 11:4)
Abraham had to believe, at his advanced years, that God would make him a father of many (Genesis 15:5-6)
Rahab had to hide the spies, at the risk of being caught and punished (Hebrews 11:31)
The point is that, by the time it reach us Gentiles, thanks to Jesus ushering the age of Grace, all we need to do, in order to display faith, is simply believing and speaking
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."
We simply believe the message, that Jesus Christ has started and completed the work required for our salvation and we cease from our work and believe it. If we do that, we will receive the same righteousness as Abraham received (Gal 3:6-9). I especially like the NLT version.
6 In the same way, “Abraham believed God, and God counted him as righteous because of his faith.”
7 The real children of Abraham, then, are those who put their faith in God. 8 What’s more, the Scriptures looked forward to this time when God would make the Gentiles right in his sight because of their faith. God proclaimed this good news to Abraham long ago when he said, “All nations will be blessed through you.”[c] 9 So all who put their faith in Christ share the same blessing Abraham received because of his faith.
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