The Covenant made as Sinai was defective in that one of the parties - Israel - was unable to live according to its terms. That made a New Covenant necessary. Although God's terms are the same for both covenants, the new one is to be written on the heart instead of on tablets of stone. The New Covenant like the one at Sinai must be ratified with the blood of a sacrifice. In this case, the blood was that of the Messiah.