Hebrews 8 explains that Jesus is the high priest of a better covenant. This covenant is superior to the old covenant because it's built on better promises. The old covenant was in effect when the first tabernacle was built, and it was carried out by the Levitical priesthood. However, Christ has established a new covenant, of which he is the mediator, and it is based on better promises. In this new covenant, God declares that he will put His commands into our minds and write them on our hearts. This is the essence of the new covenant, and it makes possible a close, personal relationship with God. Christ has become the guarantor of this covenant, which is why it can never fail. As a result, our sins are forgiven, and we can now serve the living God.