Jouette Bassler’s article on “Divine Impartiality in Romans” (NovT, 1984) also includes a neat discussion of the structure of Romans 2:12-29. She points out the sequence of terms as Paul introduces the issues of law (NOMOS) and circumcision (PERITOME). “Law” first becomes an issue in v 12, in the negative form “without law” (ANOMOS), then Paul discusses the condition of Jew and Gentile with respect to the NOMOS. In verse 25, the binary of NOMOS/ANOMOS is overtaken by another binary of circumcision/uncircumcision (PERITOME/AKROBUSTIA). Bassler argues that the “word-chain” of lawless-law-circumcision-uncircumcision unites the section.

She goes on to demonstrate the chiastic structure of this section of the chapter:

General statement (in form of not (OU) . . . but (ALLA)), vv 12-13
Conditional case A: Gentiles, vv 14-16 (the ANOMOS)
Conditional case B: Jews, vv 17-24 (those with NOMOS)
Conditional case B’: Jews, v 25 (introducing “circumcision”)
Conditional case A’: Gentiles, v 26 (“uncircumcision”)
General statement (in form of OU . . . ALLA), vv 28-29