Being a Christian all hinges on your faith in Jesus. If you believe that Jesus died to save you from persecution because of your sins, then you are saved. The OT was the God breathed word of God through Moses and the prophesy that Jesus would arrive. Christianity did not exist before the NT because Christ hadn't arrived. Even Jesus wasn't a Christian. He was a Jew. Christianity began with his birth (Christ) but mostly it was the Gentiles that believed because the Jews of the OT rejected Jesus. They had him crucified.
You cannot be accepted into eternal life without faith which translates into belief in Jesus. But you also need to prove this faith by good works. This goes hand in hand ie, if you believe you are naturally a good person willing to do good works.
This thinking sifts out those who say they believe but don't follow through with their hearts.
In the end, it's what's in your heart that matters. That's what God can see and God is about love, not anger.
But to get the eternal life in Heaven, God insists that you believe in Jesus and that his life and death were to free you from further persecution.
Read correctly, you can see that it's a love story between God and you. He wants you to accept him but not superficially by just doing lip service.
The bible and the ten commandments are a code of how to live a moral life. I can't see anything wrong in this but it's not easy for people to see it this way.
Most religions have the same core of understanding, just different ways of getting there.
In my bible dating back to the 1850's, there is a message. I think it's Leviticus. It reads 'I am the Lord your God. You are My tenant. I am your Landlord.
It speaks volumes to me about how we treat our lives, those around us and our planet.