Some ministers would like us to believe that justification and salvation by grace through faith just suddenly appeared when the Son of God lived and died in the first century. They imply that God changed His approach to saving men—that He was either losing the battle to Satan, or the way He had given man was just too hard. It also implies that men under the Old Covenant were saved by keeping the law.
Once a person has sinned, he is under the penalty of the law, and his righteousness is not sufficient to justify him before God. Since all have sinned, the whole world is guilty before God. It takes a righteousness apart from lawkeeping to do this.
Then Paul says that this righteousness is revealed in the Old Testament Law and Prophets! The teaching has been there all along, all through the centuries from Moses to Christ and down to our time! God never changed His course. In the first century, He only openly revealed the means, Christ, through whom would come the righteousness that will justify one before God.
Men have always been justified and saved by grace through faith. People who were saved during Old Testament times looked forward in faith to this being accomplished. We look backward at it as a promise and as fulfilled prophecy.