When a new act of parliament is passed into law, you expect to see some new provisions in it, some old regulations abolished, and substantial portions of the former act carried over into the new legislation. You might assume that God, likewise, when he was making a new covenant with men, would carry over into it a lot of the same provisions that were in the former covenant —some of the old is in the new. That, however, is not a good way to view the law of God.
Because of God's foreknowledge, God was able to determine what his final law would be, long before he gave any law to man. It is much better, therefore, to see foreshadowings and glimpses of the gospel in the former covenants and laws, rather than to see remnants of the former covenants in the gospel. Consider three points Paul makes in his letter to the Romans...
1 The old law was weak
In theory the law could impart life, "The one who can obey all my decrees and laws will live by them"(Leviticus 18:4-5). But in practice everyone has failed to achieve that, and in the failure has not lived but died (Romans 7:10,Romans 3:23).
Paul elsewhere speaks of "the ministry of death in letters engraved on stone"(2Corinthians 3:7). The law of Moses has never given anyone life. God had to offer another way by which people could be justified and live. He did this through Christ.
So, compared to "the power" of the gospel, God's law in former times "was weak"(Romans 1:16,Romans 8:3).
Now here's the point: if some part of old law were mixed into the new gospel law, the latter would be weakened. You cannot make a good tree stronger by grafting a weak branch into it.
2 The old law symbolized the new
The gospel existed long before the Christian age began. It was the "mystery hidden for long ages past but now revealed"(Romans 16:25,cf Eph2:10).
Regarded in that light, the gospel predates the law systems that were its precursors, and we view the law systems leading up to the gospel as containing some of the gospel. That is clearer than thinking that the gospel contains some of the laws that led up to it.
Paul’s treatment of a key passage in Deuteronomy is an excellent example of how the gospel of Christ may be found couched in the Mosaical law (Deuteronomy 30:11-16,Romans 10:5-11). Paul sees God's offer of life in the old law as symbolic of Christ The sky represents the heavenly glory from which Christ, the promised seed, would come down. The sea represents the abyss of death from which Christ would arise. The word in mouth and heart represents the gospel of faith in Christ, the faith which one confesses (Romans 10:10). in order to be buried with him in baptism and raised to walk in new life (Romans 6:3-4). and hope of a heavenly inheritance.
3 Christ is the end of the old law
Paul declares that "Christ is the end of the law"(Romans 10:4).
Elsewhere Paul tells us what Christ did with the old law: "He has taken it out of the way, having nailed to the cross"(Colossians 2:14).
How could it be that if Mosaic law is ended and dead, any of it should live on in the gospel? We can certainly find the gospel anticipated in the law of Moses. We can see that the law of Moses was influenced by the gospel and prepared people for the gospel. But now Christ has abolished the law of Moses and the gospel stands alone. It borrows nothing from the law of Moses nor is it influenced by it.