The following was written in partial fulfillment of the requirements of Dr. Heath Thomas's class at Southeastern Baptist Theological Seminary.
It is common for pastors, popular teachers, and even some scholars to treat the ‘New Covenant’ of Jeremiah 31 as something wholly distinct from the previous covenants. In this reading, the New Covenant is specific to the work of Christ in the New Testament age, and was never experienced by any “Old Testament believers”. Those believers remained under the previous (Abrahamic and especially Mosaic and Davidic) covenants, while New Testament believers are New Covenant believers. For this view, they draw on the ways that the New Covenant language was picked up by the authors of the New Testament, especially in Hebrews.
Though this reading has an ancient pedigree, going back at least as far as Jerome, it is ultimately incorrect. First, it fails to take the content of Jeremiah’s vision on its own terms. As Jeremiah traces out his vision of the New Covenant in chapters 31–33, he explicitly includes the language of law-keeping, temple working and priests, and a Davidic king over the land of Israel. These were not merely symbolic expectations, but fully fleshed out hopes for and visions of a restoration of the covenant God made with Israel at Sinai. Indeed, the terms of priestly temple sacrifice and law-keeping used throughout the section presuppose the covenant language of Deuteronomy and the discussion in Deuteronomy 30 of the circumcised heart. Thus, Hill and Walton note (and likewise Thomas suggested) that in many ways it is more appropriate to speak of a renewed covenant than of a totally new covenant.
Second, the reading of the ‘New Covenant’ as wholly new misses the ways the other authors of the Old Testament responded to this promise. In particular, Ezra’s prayer in Ezra-Nehemiah makes it abundantly clear that he considered the people’s return to the land after their 70-year-exile a fulfillment of the prophecy. If it was not a complete fulfillment—as indeed that same prayer acknowledges, for the people’s hearts were still wayward—it nonetheless represented at least a partial fulfillment. There were once again Jewish people living in the land, performing temple sacrifice and following Yahweh. Though the Davidic king had not yet been reinstated, and though the people’s hearts had not yet had the law so thoroughly stamped on them that they no longer needed teachers, the promise was partly fulfilled.
Third, even in the age after Christ’s coming it is clear that the vision remains only fulfilled in part. True: there was a significant break in the shape of history in the incarnation, life, death, resurrection, and ascension of the Son. Yet God’s law is not yet written so thoroughly on anyone’s heart that no man needs to teach his neighbor. Christians still wrestle with sin. Moreover, as the author of Hebrews notes, this Davidic king who fulfills the New Covenant hopes has not yet put everything in subjection under his feet (Heb. 2). He is seated at the right hand of God, exalted above the heavens, and has inaugurated his reign, but he has not yet consummated reign. The same author who affirms so strongly that Jesus is the fulfillment of the New Covenant hope affirms as well that the New Covenant is not yet fully completed. The ancient Jews lived in an “already but not yet” after the return from Exile. In the work of Christ, that “already” is significantly advanced—but the “not yet” remains until he returns.
This is not to say that there is nothing new about the New Covenant. Unlike in Deuteronomy 30, where the people were enjoined to repent and circumcise their own hearts, the work in Jeremiah’s vision is wholly God’s. Too, the New Testament’s embrace of New Covenant language in terms of Jesus’ work means that Christians should understand that something new has happened in Christ. Specifically, Christ has done what Israel could not. Jesus kept the law perfectly, needing no one to teach him; he served as both priest and sacrifice to make atonement for the sins of the people; he rules and judges righteously as the Davidic Branch who represents Yahweh; he even reconstituted Israel in his twelve disciples. Jesus Messiah is the fulfillment of the New Covenant. He is the hope toward which the Old Testament saints looked.
Augustine, not Jerome, had the right of it. All the Old Testament saints were participants in the New Covenant. They looked forward to that which they did not see, but they too were saved by faith in Christ. They did not have the full revelation with which New Testament saints are blessed. They saw from far off that of which Christians now enjoy the fullness. But Jesus’ work in bringing about the New Covenant was not something foreign to the covenants that had gone before; it was the fulfillment of all of them. Here was the offspring of the woman who would crush the serpent’s head, the offspring of Abraham in whom all nations would be blessed, the prophet like Moses who would give the law anew, the true Israel who would keep the law rightly, the offspring of David who would do justice for his people and for the nations. Jeremiah’s New Covenant promised the fulfillment of what had gone before. It was new in that Jesus finally accomplished what no Israelite ever had. It was the renewal of the old in that what Jesus accomplished was precisely the hope set before Israel from the beginning.