I have spoken about the Old Covenant and its relationship to Jesus and the New Covenant (see my video here)
The law and the prophets were until John. Since that time the kingdom of God has been preached, and everyone is pressing into it. 17 And it is easier for heaven and earth to pass away than for one tittle of the law to fail.
God is always accomplishing His plan. He gave the world the Law and the Prophets leading up to John the Baptist who would prepare the way for Jesus Christ, the embodiment of all God was doing. He died, once for all, so that we would not need to meet the obligations of God’s righteousness (which we can’t) in order to be righteous before God. That’s the gospel, we are saved by what Jesus did, not by what we can do.
This is the difference in Christianity, it is not how you can clean yourself up, it is not about you doing right… Christianity is about how if you cling to Jesus, he will save you!