A.T. Robertson Commentary Romans 2:29

"but he is a Jew who is one inwardly; and circumcision is that of the heart, in the spirit not in the letter; whose praise is not of men, but of God." — Romans 2:29 (ASV)

Who is one inwardly (ο εν τω κρυπτω). Repeat Ιουδαιος (Jew) here also, "the in the inward part Jew" (circumcision of the heart περιτομη καρδιας and not a mere surgical operation as in Col 2:11, in the spirit εν πνευματ, with which compare 2 Corinthians 3:3,6). This inward or inside Jew who lives up to his covenant relation with God is the high standard that Paul puts before the merely professional Jew described above.

Whose praise (ου ο επαινος). The antecedent of the relative ου is Ιουδαιος (Jew). Probably (Gifford) a reference to the etymology of Judah (praise) as seen in Ga 49:8.