Why weren't Old Testament people expected to believe that Christ would die and rise again?

Les explains that the secret things belong to the Lord God because He is sovereign. God does not tell us everything we might like to know; He tells us everything we need to know, but in His own time. Therefore, Adam and Eve and Abraham did not understand the gospel, since God had not yet revealed it. It was kept secret, held in the mind of God, not to be revealed until much later. So Old Testament people were not expected to believe that Christ would die, be buried, and be raised from the earth, even though the Old Testament was full of it by innuendo at least. The reason is that you do not believe something until God says it. Once God reveals something, however, it belongs to us and our children. Les then applies this: when God revealed the gospel of the grace of God—that all we must do is believe Christ died, shed His blood, was buried, and rose from the dead—He expects us to believe it. Salvation is by faith plus nothing in what He has now proclaimed. Faith comes by hearing the Word of God.