1. τί οὖν ἐροῦμεν = what shall we say of Abraham?…, i.e. in relation to the question of boasting and the source of righteousness. Zahn (Einl. p. 95, A2) punctuates ἐροῦμεν; and takes [εὑρ.] Ἀβραὰμ … θεόν as stating an opposed view: but this is too complicated.
τὸν προπάτορα ἡμῶν. Addressed to Gentiles (as well as Jews); cf. 11, 12 and 1Co 10:1. The spiritual lineage is an essential strain in S. Paul’s conception of religious history.
κατὰ σάρκα. If this goes with προπάτορα then the whole clause must be taken as a difficulty raised by a supposed Jew disputant. But it is better taken with ἐροῦμεν in relation to ἐξ ἔργων of Rom 4:2 and περιτομή, Rom 4:9 ff. = as regards his human condition—his works and the covenant of circumcision; cf. Hort, R. and E., p. 23.