We have to remember that the Sinai covenant is not simply identical to the pre-fall Adamic covenant. The very purpose of the Jewish theocracy was to point forward through types to the coming Messiah. The very purpose of the Jewish theocracy was to point forward through types to the coming Messiah. This typological kingdom could not be maintained by God, if the existence of the kingdom was dependent on perfect obedience.
There are similarities between near-eastern treaty custom and the covenant God made with Israel. However, there are definite differences between this biblical covenant and secular covenant like the Hittites’ covenant. The chapter 2 of this book briefly explores this similarity and difference between biblical and secular covenants.
The chapter 3’s main focus is on answering questions: “Are there two different covenant traditions?”
So Mosaic covenant and Abrahamic covenant are both different administration of the same covenant of grace.
“While there are more than two covenants in the Scriptures, they all can be ground around two arrangements: conditional covenants that impose obligation and unconditional covenant that announce divine promise…
In Galatians 4, Paul has two “laws” in mind which he actually calls “covenants”
A covenant of law, which promise blessing upon perfect obedience and curses for any transgression, and a covenant of promise, which promises blessing as a gift resulting from the personal performance of another.”
The precise nature of two covenants: Sinai covenant(covenant of law) and Abrahamic covenant(covenant of promise)
“It is as if, from the divine side, the covenant made with Abraham is a suzerainty treaty in which God swears unilaterally to personally perform all of the conditions and suffer all of the curses for its violation, but from the human side, the same covenant is a royal grant, an inheritance freely given and in utter graciousness on the basis of the Great King’s performance.”