What is a covenant? A covenant is an agreement with two unequal parties. Covenants were a vital part of the culture in the early times of mankind. The king would make a covenant with his vassal, someone who couldn't give him anything in return, and the king would be bound to keep his promise. God made a covenant with Abraham, and the bible gives us a description of that covenant.
God gives us a vision of the covenant between him and Abraham. Abraham has divided animals in half and placed them opposite each other. Then in his vision he sees a torch and a pot pass between them. This was a binding covenant. God was saying if I break my promise to you, then I shall be torn in half just like these animals. That's a powerful thing! And remember, God had no one more powerful to swear by so He made the promise by Himself! God cannot break this promise. That's the entire concept of the covenant.
Yet it also shows us that there is a blessing AND a curse. If we break the covenant, we will be just like those animals, dead. This is why the wages of sin is death. If we break our promise to God, we deserve death. And the bible tells us ALL have sinned. In fact, if we examine our consciences we know we have sinned. God also made a covenant with Moses at Sinai. This is what most refer to as the Old Covenant. It begins with the ten commandments, and when all is said and done contains 612 different rules and regulations. Imagine that! 612 different things you have to follow to stay in good standing with God! So what does the old covenant have to do with us?
The Bible tells us that when Jesus was on the cross, He became the curse for us. That doesn't mean that Jesus was the curse. It means that HE took our curse. That is why it tells us that Jesus fulfilled the old covenant. Because we could not keep the sin free life, we deserved the curse, death. So Jesus took it in our place! He died for us that the covenant would be fulfilled.
That is also why Paul says if we go back under the Old Covenant, we have to keep ALL of it. Because if we do not, we are breaking the covenant.. and instead of a blessing we will receive the curse. It's how a covenant works! It doesn't change, it isn't gone.. the law is still there.. but we aren't under the law, we are under the New Covenant, the Covenant of grace.
That doesn't make us free to do whatever we want. We have our own moral codes to try and live by, but if anyone tells you that you have to follow the Old Law to be sealed into God, or that we have to receive a mark that involves the Old Law, and not the New, then if we follow the Old Covenant, we have to follow all 612 commands, not just 10 or 1.
Does that mean the ten commandments are bad? No. They are a beautiful way of judging morality and we should indeed use them in our lives. But we aren't 'under' them. They are not our seal with God. The Bible clearly tells us that the seal of God is the Holy Spirit. So go forth, continue to learn what the New Covenant is, and how the early church formed. Study the early church fathers and their works, and find out what the covenant we are under means to us. It's not free or cheap grace, but it's still a light burdern and easy yoke.
Was Abraham's the only covenant? How many different covenants are there in the old testament? What are some of the 'signs' of those covenants? What is the sign of the Christian covenant?