How many times have people welcomed you to church by saying, "Welcome to the House of the Lord." Yet that's not a New Testament teaching. It's an Old Testament point of view, when God's presence filled the holy of holies of the Temple in Jerusalem. But that all ended with the coming of the Holy Spirit and the destruction of the brick and mortar Temple by the Romans. The apostles tell us believers are the Temple of God now, living stones built up together into a living Temple where God dwells. So why do we persist in saying the building is the Temple when the Biblical teaching is that the people are the Temple?
Have you noticed how some people are saying we should go back to keeping the Sabbath (and not just Seventh Day Adventists)? Some have gone so far as to insist the passage where Jesus says, "Many will say to me Lord, Lord, and I'll say to them, I never knew you, depart from me you workers of iniquity," is referring to people who don't keep the Sabbath. In other words, faith in Jesus and his Cross and Resurrection isn't enough, no, you have to keep the Sabbath too, and then you can be saved. There is no New Testament support for such a position. Jesus himself broke the Sabbath by eating and healing on Saturdays. He asserted that he was Lord of the Sabbath and that the Sabbath wasn't Lord of him. He also insisted that the Sabbath was made for humans, to bless them, and that humans weren't made to serve the Sabbath as if it were some kind of deity. Yet some Christians persist that we were meant to serve the Sabbath and God won't bless us until we do.
The Old Testament is what you follow if you embrace Judaism. Jesus may have used the Greek version of the Old Testament as his Bible but everything changed with his coming and with his Crucifixion and the descent of the Holy Spirit at Pentecost. As the apostles wrote gospels and letters a new Bible was formed, a New Testament. It is through Jesus, the Messiah, and the New Testament that we look back at the Old Testament and view its prophecies and teachings. Jesus interprets its proper meaning for us - "You have heard it said (in the Old Testament) such and such a thing, but I say to you that it's different now and that the fulfillment of the Law is found in grace, mercy, love and justice, not more rules, and not a Law that acts as if the Messiah hasn't come."
For indeed this present-day "back to the Old Testament" movement is just another version of the people Jesus clashed with and the apostles, people who said you couldn't find God if you weren't circumcised, didn't keep the Sabbath, didn't eat kosher according to the dietary laws found in Leviticus, didn't keep the commandments and the Law, didn't follow the holy feast days. But this is not Christianity - it's Judaism. If you want to convert and be a Jew, go ahead, but don't call it Christianity because it's the farthest thing from Christianity. Jesus and his teachings are authoritative for the Christian, not an Old Testament quoted and utilized as if Jesus the Messiah has never come and transformed and fulfilled everything. The Law may have come with Moses but grace and truth came with the Messiah and it's that grace and truth that a Christian lives by, not the teachings of Moses.
We learn from the Old Testament. We understand its true meaning by way of Jesus and the New Testament. But we do not take it on its own as if Jesus never came. We don't run around talking about "eye for eye, tooth for tooth" as if Jesus didn't change the whole meaning of that verse. We bear in mind that if the Law and the Old Testament could save then there was no reason for Jesus to come and die on the Cross. There would have been no reason for 1st century Jews to repent and worship Jesus, they could have just stuck to Moses. Jesus came because the Old Testament was not enough and could not save and it's still not enough and still can't save. Redemption in its pages only lies in embracing the prophecies of the Messiah and worshiping Jesus as Redeemer and Lord and God. Not in following the Old Testament Law that saved no one and still doesn't.
In the spirit of Jesus, and through his eyes, we can learn what we're meant to learn from the Old Testament, and there's much that can be learned if we approach the Hebrew Scriptures properly. But it is not the book Christians live by and establish as their sole authority. The New Testament is authoritative for Christians and it is Jesus and his words Christians live by. There is a big difference between Old and New and returning to live under the Law is spitting, in my opinion, on the Cross of Jesus Christ and thereby rejecting the heart and soul of the Christian faith.