Since the fall of man, not that God revised and re-revised His plan of salvation over the ages for the fallen mankind. No. Salvation has always been the same—it is by God’s grace through faith which He planned right from the beginning to be achieved through the death of Christ. No one, either prior to the cross or since the cross, would ever be saved without that one pivotal event in the history of the world. Christ's death paid the penalty for past sins of Old Testament saints and future sins of New Testament saints.
The major difference is that before Christ’s earthly life, salvation was found in faith in the Lord. Adam and Eve, for example, had faith in God and fellowship with Him. Abraham trusted the Lord by faith. Genesis 15:6 tells us that Abraham believed God and that was enough for God to credit it to him for righteousness.
Hebrews 11 provides an entire chapter of people who followed the Lord by faith, not knowing the details of the Christ who would come.
The Old Testament sacrificial system did not take away sin, as Hebrews 10:1-10 clearly teaches. It did, however, point to the day when the Son of God would shed His blood for the sinful human race.
For since the law has but a shadow of the good things to come instead of the true form of these realities, it can never, by the same sacrifices that are continually offered every year, make perfect those who draw near
Jesus was the fulfilment of the Old Testament sacrificial system, the one Savior who permanently restores relationship with God.
God's plan of salvation
God's requirement of what must be believed is based on the amount of revelation He has given mankind up to that time. Adam believed the promise God gave in Genesis 3:15 that the Seed of the woman would conquer Satan. Adam believed Him, and demonstrated it by the name he gave Eve Genesis 3:20 and the Lord indicated His acceptance immediately by covering them with coats of skin Genesis 3:21. At that point that is all Adam knew, but he believed it.
Abraham believed God according to the promises and new revelation God gave him in Genesis 12 and 15. Prior to Moses, no Scripture was written, but mankind was responsible for what God had revealed. Throughout the Old Testament, believers came to salvation because they believed that God would someday take care of their sin problem.
Late in His ministry, “Jesus began to explain to his disciples that he must go to Jerusalem and suffer many things at the hands of the elders, chief priests and teachers of the law, and that he must be killed and on the third day be raised to life” (Matthew 16:21-22). At this Peter took him aside and began to rebuke him. ‘Never, Lord!’ he said. ‘This shall never happen to you!’” Peter and the other disciples did not know the full truth, yet they were saved because they believed that God would take care of their sin problem. They didn't exactly know how He would accomplish that, any more than Adam, Abraham, Moses, or David knew how, but they believed God.
Today, we look back, believing that He has already taken care of our sins on the cross (John 3:16; Hebrews 9:28).
Prior to Jesus, salvation was based on faith in God and trust in His plan. Ultimately, it was still based on the death and resurrection of Christ, though God’s followers did not know exactly how that would look. Today, knowing that Jesus died for our sins, was buried, and rose the third day (1 Corinthians 15:3-4), the content of our faith is a bit more specific. However, faith is still the requirement for salvation, the object of our faith is still God, and the completer of our salvation is still Jesus.