From The Christ of the Covenants, O. Palmer Robertson, pg. 41.
The New Covenant, promised by Israel’s prophets, does not appear as a distinctive covenantal unit unrelated to God’s previous administrations. Instead, the New Covenant as promised to Israel represents the consummate fulfillment of the earlier covenants. This organic relation of the New Covenant to the covenants of Abraham, Moses, and David finds explicit development both in the Old Testament prophecies concerning the covenant and in the New Testament realizations of this consummating covenant. From either perspective, the New Covenant may be understood in no other way than as a realization of the prophetic projections found in the Abrahamic, Mosaic, and Davidic covenants.
Jeremiah’s classic prophecy clearly relates the New Covenant to its Mosaic predecessor (cf. Jer. 31:31 ff.). This “New Covenant” with the “house of Israel and with the house of Judah” will not be like the Mosaic covenant in its externalistic features. But the law of God as revealed to Moses shall be written on the heart. While the substance of the law will be the same, the mode of its administration will be different. The form may change, but the essence of the New Covenant of Jeremiah’s prophecy relates directly to the law-covenant made at Sinai.
In the following chapter, Jeremiah combines a reference to the New Covenant with allusion to the ancient covenant made with Abraham. God will “faithfully plant” his people “in this land” (Jer. 32:41). But at the same time he will “give them one heart and one way” that they may fear him always (Jer. 32:39, 40). By the intertwining of these references, the prophet combines the Abrahamic with the New Covenant. These two covenants unite to form a single expectation for God’s people.3