Imperative. It may also be rendered as indicative, ye know, but the imperative is livelier, and the statement in the verse is one of the points which the writer is trying to prove.
They which are of faith (οἱ ἐκ πίστεως)
Ἑκ πίστεως from or out of faith, is found with the verb to justify (Rom 3:26, Rom 3:30; Rom 5:1): with other verbs, as live (Rom 1:17); eat (Rom 14:23): with the noun δικαιοσύνη righteousness (Rom 1:17; Rom 9:30; Rom 10:6): with other nouns, as promise (Gal 3:22), law (Gal 3:12). For parallels to the phrase οἱ ἐκ πίστεως, see Rom 3:26; Rom 4:16; Rom 14:23; Gal 3:9. It denotes believers as sprung from, or receiving their spiritual condition from that which specially characterizes them. Comp. οἱ ἐξ ἐριθίας they who are of faction, Rom 2:8; οἱ ἐκ νόμου they who are of the law, Rom 4:14; ὁ ἐκ τῆς ἀληθείας he who is of the truth, Joh 18:37.