Rom 2:17–18 and Jer 9:23–24 (MT 9:22–23): boasting and knowing God

Says Rom 2:17–18 addresses one who καυχᾶσαι ἐν θεῷ ("boast in God") and γινώσκεις τὸ θέλημα ("know the will").

Says Jer 9:23–24 (MT 9:22–23) forbids the wise, the mighty, and the rich to boast, אַל־יִתְהַלֵּל (al-yithallel, "let him not boast"; BDB p. 239, Hithpael "glory, boast"), but בְּזֹאת יִתְהַלֵּל הַמִּתְהַלֵּל הַשְׂכֵּל וְיָדֹעַ אוֹתִי (bezo't yithallel hammithallel haskel veyadoa' oti, "in this let the one who boasts boast: understanding and knowing me"), that the Lord practices steadfast love, justice, and righteousness, כִּי־בְאֵלֶּה חָפַצְתִּי (ki-ve'elleh khafatsti, "for in these I delight"). Swete's LXX (9:24): ἐν τούτῳ καυχάσθω ὁ καυχώμενος, συνίειν καὶ γινώσκειν, ending ὅτι ἐν τούτοις τὸ θέλημά μου, with θέλημα for "I delight."

Says The next verses (9:25–26) threaten the circumcised who are uncircumcised in heart, with Judah listed among the nations.

Implies Rom 2:17–18 echoes Jer 9:23–24. LXX Jer 9:24 shares boasting, knowing, and God's θέλημα (καυχάσθω, γινώσκειν; cf. καυχᾶσαι, γινώσκεις), and Paul knew the verse as a word about boasting: he quotes it in short form at 1 Cor 1:31 and 2 Cor 10:17. Jer 9:23–26 also moves from true boasting to circumcision of the heart, as Rom 2:17–29 does. The words are common, however, and Paul gives no marker.