The difference between the old and new covenants is that the old was conditional and the new is unconditional. Compare Heb. 8:9 with 8:11. 'For they shall all know Me, from the least of them to the greatest of them. 'The most prominent feature of the Sinaitic ('first,' 'old') covenant is the law. It is interesting to observe its conditional nature in contrast to the 'covenants of promise' (Eph. 2:12).
Gen 9:11 (Noahic). Thus I establish My covenant with you: Never again shall all flesh be cut off by the waters of the flood.”
Gen 12:2 (Abrahamic). “I will make you a great nation; I will bless you and make your name great; and you shall be a blessing……….And in you all the families of the earth shall be blessed.”
1Chron 17:11 (Davidic). “And it shall be, when your days are fulfilled, when you must go to be with your fathers, that I will set up your seed after you, who will be one of your sons; and I will establish his kingdom.”
Exod 19:5 (Sinaitic). “Now therefore if you will indeed obey My voice and keep My covenant, then you shall be a special treasure to Me above all people.”
The “I will” of the covenants of promise contrasts with the “if you will” of the Sinaitic. Note also the “He will” when the New Covenant is announced.
Matt 1:21. “…..And you shall call His name Jesus for He will save His people from their sins.”
Luke 1:32. “He will be great and will be called the Son of the Highest; and the Lord God will give Him the throne of His father, David.”
‘For all the promises of God In Him are Yes, and in Him, Amen, to the glory of God’ (2Cor 1:20). The covenants of promise are fulfilled in Christ.