The New Covenant promised to Israel and Judah in Jeremiah 31:31–34 includes two components that some argue are fulfilled by the church. In Jeremiah 31:33, “I will put My law within them and on their hear I will write it…” and in Jeremiah 31:34, “They will not teach again his neighbor and each man his brother, saying, ‘Know the Lord.’ For they will all know Me, from the least of them to the greatest.’”
Romans 2:29 reads, “But he is a Jew who is one inwardly; and circumcision is that which is of the heart, by the Spirit, not by the letter…” Does this passage represent even a partial fulfillment of the New Covenant promise? Does it redefine what it is to be a Jew? No and no. First, in Romans 4, Paul explains that there are several ways in which Abraham is a father: a forefather according to the flesh (4:1), the father of circumcision to those who are both of the circumcision and who follow in his faith (4:12), and father to all who are of faith (4:16). Paul later explains that not all who are descendants according to the flesh are counted as Israel (9:6-7). In other words, in these contexts, Paul identifies three kinds of descendants: those who are only fleshly descendants, those who are both fleshly and spiritual (of faith) descendants, and those who are only spiritual (of faith) descendants.
While Paul seems to be referring to aspects similar to those of the New Covenant (in that the Spirit is affecting the heart), the allusion is not the same as fulfillment. Paul is not referencing, in this context, either those who are only fleshly descendants of Abraham but who do not have faith, nor those who are only spiritual descendants and who have faith, but are not physically descended from Abraham through the lines of Isaac and Jacob. In other words, Paul is not talking about either unbelieving Jews or believing Gentiles. Instead, he is identifying those who are both physical descendants (through Isaac and Jacob, and therefore who are Jews outwardly) and spiritual descendants (those having faith) – believing Jews.
Consequently, he is not identifying all church–age believers as somehow fulfilling the New Covenant, nor is he suggesting the New Covenant is being fulfilled now. Jeremiah 31:33 requires not just that there be an internal working of the Spirit on the heart, but specifically that He would write His law on their hearts. The two are not the same. In 2:15 Gentiles who do the things of the Law are said to “show the work of the Law written in their hearts,” but “of the Law” is in the genitive and modifies “works.” The “works” are written on the hearts, not the Law itself. The work of the Holy Spirit in previous ages and in the current one bears similarity to His New Covenant ministry, but in each case, His work is still markedly different than in the New Covenant.
First John 2:27 reads, “As for you, the anointing which you received from Him abides in you, and you have no need for anyone to teach you; but as His anointing teaches you about all things, and is true and is not a lie, and just as it has taught you, you abide in Him.” Some view this as indication that the Jeremiah 31:34 promise is currently being partially or fully fulfilled, but what is described in 1 John 2:27 is very different from the Jeremiah promise. The former is addressed to those who believe in Jesus Christ (1 Jn 5:13). The teaching in Jeremiah 31:34 is related to knowing Him, and the reference is to a time when all Israel will know Him – all Israel will be saved (e.g., Rom 11:26–27). John writes only to believers, describing something exclusive for them (“the anointing you received”), while Jeremiah’s prophecy describes a national salvation for all Israel (“for they will all know Me, from the least of them to the greatest of them”). Again, while there is similarity between these two ideas, the two are not the same.
Just as in the physical creation, where there are similarities between various components, there are similarities in components of God’s prophetic plan. For example, there is a prophecy that Saul would rule over Israel (1 Sam 9:15–16), and there is a prophecy that Jesus would rule over Israel (e.g., Lk 22:30; Rev 20:1ff), but we wouldn’t equate the two simply because there are similarities. Neither would we equate Adam with Ananias and Sapphira simply because they shared the experience of death. All Christians have the indwelling Holy Spirit (Rom 8:9, Eph 1:13–14), and the Holy Spirit will have an active role in the fulfillment of the New Covenant. Just as we can’t too closely associate Saul and Jesus, or Adam and Ananias and Sapphira, we need to be cautious about drawing unjustified connections between the church and the New Covenant.