How Is The Atonement Applied to Old Testament Saints?

This has been one question that has perplexed a lot of Christians. We know the New Testament teaches that when one puts their faith and truth in Christ alone they are saved. What about the saints in the Old Testament like Abraham, Issac, Joseph, Moses, and David? How does the atonement apply to them since they died before the coming of Christ? R.C. Sproul addresses this issue in his book, The Truth of the Cross:

The answer to this question is clear from Scripture. The people who lived in Old Testament times had the sacrificial system, but the blood of bulls and goats didn't atone for anyone. These things pointed the people of Israel beyond themselves to an atonement that would satisfy the righteousness of God. The Old Testament person who trusted the promise of the work of the Messiah, even though that work had not yet been accomplished in space and time, was saved. The ground of that salvation was the work of Christ that was yet to come. Old Testament believers were saved by a faith that looked forward, while we are saved by a faith that looks backward. The objective ground for salvation of both groups is the same - the atonement of Christ.