“He [Jesus] is the mediator of a better covenant, which was established upon better promises” (Hebrews 8:6).
Jesus is the mediator of a better covenant than the one received through Moses. It is a better covenant because it is founded on better promises. The covenant of law (the Ten Commandments, etc.) promised blessing for obedience but threatened death for disobedience. It required righteousness, but did not give the ability to produce it.
The new covenant is an unconditional covenant of grace. It imputes righteousness where there is none. It teaches men to live righteously, empowers them to do so, and rewards them when they do.
—William MacDonald, from Hebrews: From Ritual to Reality.