δικαιοῦσθαι πίστει … χωρὶς ἔργων νόμου; ἐκ πίστεως / διὰ τῆς πίστεως

Says 3:28: λογιζόμεθα γὰρ δικαιοῦσθαι πίστει ἄνθρωπον χωρὶς ἔργων νόμου (BSB "For we maintain that a man is justified by faith apart from works of the law"). πίστει (pistei) is a dative of means, ἄνθρωπον is generic ("a person"), and χωρίς means "apart from." On γάρ/οὖν and the word order see var.Rom.3.28.gar-oun and var.Rom.3.28.pistei-order.

Implies "Faith alone" is a fair summary of 3:28. Grounds: justification is by faith "apart from works of the law" (3:28), "freely by His grace" (3:24), with boasting excluded (3:27), and is credited to the one who does not work (4:4–5). The Exegete's commentary carries the sentence on Luther and the paragraph on "works of the law."

Says 3:29–30: ἢ Ἰουδαίων ὁ θεὸς μόνον; οὐχὶ καὶ ἐθνῶν; ναὶ καὶ ἐθνῶν, εἴπερ εἷς ὁ θεός. εἴπερ is most likely causal here, "since," though it can mean "if indeed" (var.Rom.3.30.eiper-epeiper). The echo of the Shema is treated by the Hebrew Scholar (note.language.Rom.3.30.shema).

Uncertain ἐκ πίστεως (the circumcised) and διὰ τῆς πίστεως (the uncircumcised). This note leans to a stylistic variation with no difference in sense: Paul uses both prepositions with πίστις of the same justification (3:22, 26; Gal 2:16), and the article in διὰ τῆς πίστεως is anaphoric (BSB "that same faith"). The main alternative is a deliberate distinction between Jew and Gentile.