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 Colossians 2:11, in the spirit εν πνευματ, with which compare 2. Corinthians 3:3; 2. Corinthians 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 Galatians 49:8. 

Romans 3:1

What advantage then hath the Jew? (τ ουν το περισσον του Ιουδαιου?). Literally, "What then is the overplus of the Jew?" What does the Jew have over and above the Gentile? It is a pertinent question after the stinging indictment of the Jew in chapter 2.

The profit (η ωφελια). The help. Old word, only here in N.T. See Mark 8:36 for ωφελε, the verb to profit.