Why do we still practice old testament doctrine whilst Christ is the end of the law Romans 10:4 and He (Jesus) fulfilled it on the cross when He (Jesus) said ”it is finished” John 19:30. James 2:10 says the law is a unit if you obey one you must obey all and Christ is the only one who obeyed the law to the letter.
His truth endureth to all generations. So the truth of yesterday is the truth of today, and it’s the truth of tomorrow.
We don’t practice Old Testament laws. We practice what God has said we should do. But what you need to understand is that everything Paul quoted in the New Testament was from the Old Testament.
The scripture, the real Word of God is the Old Testament. The difference is the mediator. Moses was the mediator of the Old Testament but he did not die for our sins. Jesus is the mediator of the New Testament. The difference is also in the sacrifice. In the Old Testament it was the blood of bulls, and in the New Testament it is the blood of Christ, once and for all. But every other things still follows, Jesus fulfilled it (every scripture that was quoted even by Jesus, Peter, etc; it wasn’t as if new scripture was written from heaven). What Jesus did was establish the Old Testament with the new blood.