Living according to the letter of the law denies the real fact that the Christian has died in Christ–has died to sin and has died to the law. Paul is not blowing smoke when he says that we have been crucified with Christ (Galatians 2:20; Colossians 2:20), and our life is hid with Christ in God (Colossians 3:3), having been made alive with Christ. (Ephesians 2:5) And if we are raised with Christ, we are now to seek the things that are above (Colossians 3:1), not being pre-occupied with religious observances (Colossians 2:20) which can not save or perfect us, but that merely teach about spiritual truths. We are buried and raised with Christ in baptism (Colossians 2:12), and through baptism into Christ’s death (Romans 6:4) we are dead to the law (Romans 7:4) and have been unshackled from the law. (Romans 7:6)
The difference between God’s people the Israelites and God’s people the Christians is in their baptism. The Israelites were baptized unto Moses as their lawgiver in the cloud and in the sea (1 Corinthians 10:2) at the Red Sea crossing. And their inheritance in the land was bound up in their obedience to the law of Moses. (Deuteronomy 6:17-18) We are baptized into Christ as our lawgiver, and the Adamic man is destroyed so the the Mosaic law has no more jurisdiction over us, only the spiritual law of God. The law has dominion over a man as long as he lives, (Romans 7:1) and no longer. So anything that puts a Christian under the law of Moses is anti-Christ and anathema.