The Revelation of Jesus and Sacrifice for Sin
This is the heart of both the Old Testament, which Jesus said spoke of Him in type and prophecy, and the New Testament, which gives the biblical record of His coming. The promise of blessing is dependent on grace and mercy given to the sinner. Grace means that sin is not held against the sinner. Such forgiveness is dependent on a payment of sin's penalty to satisfy holy justice. That requires a substitute - one to die in the sinner's place. God's chosen substitute - the only one who qualified - was Jesus. Salvation is always the same gracious means, whether during Old Testament or New Testament times. When any sinner comes to God, repentant and convinced he has no power to save himself from deserved judgment of divine wrath, and pleads for mercy, God's promise of forgiveness is granted. God then declares him righteous because the sacrifice and obedience of Christ is put to his account. In the Old Testament, God justified sinners that same way, in anticipation of Christ's atoning work. There is, therefore, a continuity of grace and salvation through all of redemptive history. Various covenants, promises, and epochs do not alter that fundamental continuity, nor does the discontinuity between the Old Testament witness nation, Israel, and the New Testament witness, people, the church. A fundamental continuity is centered in the Cross, which was no interruption in the plan of God, but is the very thing to which all else points.
Throughout the Old Testament, the Savior and sacrifice are promised. In Genesis, He is the seed of the woman who will destroy satan. In Zechariah, He is the pierced one to whom Israel turns and by whom God opens the fountain of forgiveness to all who mourn over their sin. He is the very One symbolized in the sacrificial system of the Mosaic law. He is the suffering substitute spoken of by the prophets. Throughout the Old Testament, He is the Messiah who would die for the transgressions of His people; from the beginning to end in the Old Testament, the theme of the Lord and Savior as a sacrifice for sin is presented. It is solely because of His perfect sacrifice for sin that God graciously forgives repentant believers.
In the New Testament, the Lord and Savior came and actually provided the promised sacrifice for sin on the Cross. Having fulfilled all righteousness by His perfect life, He fulfilled justice by His death. Thus God Himself atoned for sin, at a cost too great for the human mind to fathom. Now He graciously supplies on their behalf all the merit necessary for His people to be the objects of His favor. That is what Scripture means when it speaks of salvation by grace.