The main purpose of the Old Testament institutions was to show the truth that remission and forgiveness is wholly wrapped up in the Lord Christ, and out of Christ nothing at all can be known of God's pardoning mercy and nor can the least morsel of it be tasted apart from Christ. If God had not set forth the Lord Christ, all the angels in heaven and men on earth could not have known that there had been any such pardoning mercy in the nature of God.
Paul teaches that in Christ the full revelation as well as the exercise of this mercy is to be seen in Christ alone, both in his being sent and his being declared and preached in the gospel. So this pardoning mercy and salvation was not discovered by good works.
John Owen, Communion With God