There are two parts to Paul’s argument here. First, he takes up the warning found in Jeremiah that physical circumcision alone will not safeguard Israel from the wrath of God:

Circumcise yourselves to the Lord; remove the foreskin of your hearts, O men of Judah and inhabitants of Jerusalem; lest my wrath go forth like fire, and burn with none to quench it, because of the evil of your deeds. (Jer. 4:4)

Thus says the Lord: “Let not the wise man boast in his wisdom, let not the mighty man boast in his might, let not the rich man boast in his riches, but let him who boasts boast in this, that he understands and knows me, that I am the Lord who practices steadfast love, justice, and righteousness in the earth. For in these things I delight, declares the Lord.” “Behold, the days are coming, declares the Lord, when I will punish all those who are circumcised merely in the flesh….” (Jer. 9:23-25)

We must still think of this ‘wrath’ of God in concrete historical rather than metaphysical terms. Jeremiah envisages a time when ‘Besiegers come from a distant land; they shout against the cities of Judah’ (Jer. 4:16), when ‘death has come up into our windows; it has entered our palaces, cutting off the children from the streets and the young men from the squares’ and the ‘dead bodies of men shall fall like dung upon the open field…’ (Jer. 9:21-22). What will safeguard the status and integrity of Israel in this historical and eschatological sense will be the inward circumcision of the heart that will lead to the abandonment of evil deeds and a commitment to practice ‘love, justice, and righteousness in the earth’ in which the Lord delights. This will be the ‘new covenant with the house of Israel and the house of Judah’, written on the hearts of the people (Jer. 31:31-34; 32:40).

Secondly, the converse possibility arises that Gentiles who are uncircumcised will nevertheless keep the precepts (dikaiōmata) of the law and on the day of wrath in some sense stand in judgment over Israel, which, despite being circumcised as a sign of being God’s covenant people, has failed to keep the terms of that covenant. The rationale for this startling revision is to be found in Ezekiel 36:26-27 LXX:

And I will give to you a new heart and I will give a new spirit among you, and I will take out the heart of stone from your flesh and I will give you a heart of flesh. And I will give my Spirit among you, and I have done (this) in order that you may walk in my statutes (dikaiōmasin) and keep my judgments and do (them).

The covenant is renewed for the sake of the righteousness of the people of God – so that they may walk in his statutes and keep his commandments. But if this is done through a renewal of the heart, the name ‘Jew’ and the physical sign of circumcision must be reapplied. They are given, in Paul’s sharpened rhetoric, to those who have entered into this new covenant.