It was never intended to save. O.T. was focused in one direction - the later completion of God's plan of redemption. But to the O.T. saints - it was like the pieces of a puzzle that didn't make sense. Not spoken all at once. The pieces begin to come together in Genesis 3.
Sin has a cost.
In you all the families of the earth will be blessed. Issac, Jacob, Moses, David Piece by piece puzzle began to fall in place - but prophets still couldn't understand all that God was going to do. These all died in faith, not having received the promises, but having seen them afar off were assured of them, embraced them and confessed that they were strangers and pilgrims on the earth. Mt. Olivet Is. We see God has been at work all along to provide my redemption.