Okay, A common misconception about the Old Testament way of salvation is that Jews were saved by keeping the Law. But we know from Scripture that that is not true.
In Romans 4 the Apostle paul makes it very clear that the Old Testament way of salvation was the same as the New Testament way, which is by grace alone, through faith alone, in Christ alone. To prove this, Paul points us to Abraham, who was saved by faith: “Abraham believed God, and it was credited to him as righteousness” (Romans 4:3). Again, Paul quotes the Old Testament to prove his point—Genesis 15:6, this time. Abraham could not have been saved by keeping the Law, because he lived over 400 years before the Law was given!