When they opposed themselves (antitassomenōn autōn). Genitive absolute with present middle (direct middle again) of antitassō, old verb to range in battle array (tassō) face to face with or against (anti). In the N.T. only here and Rom 13:2; Jam 4:6; 1Pe 5:5. Paul’s fresh activity roused the rabbis as at Antioch in Pisidia and at Thessalonica in concerted opposition and railing (blasphemy).
He shook out his raiment (ektinaxamenos ta himatia). First aorist middle of ektinassō, old verb, in the N.T. only here as in Act 13:51 (middle) and Mar 6:11; Mat 10:15 where active voice occurs of shaking out dust also. Vivid and dramatic picture here like that in Neh 5:13, “undoubtedly a very exasperating gesture” (Ramsay), but Paul was deeply stirred.
Your blood be upon your own heads (To haima humōn epi tēn kephalēn humōn). As in Eze 3:18., Eze 33:4, Eze 33:8.; 2Sa 1:16. Not as a curse, but “a solemn disclaimer of responsibility” by Paul (Page) as in Act 20:26. The Jews used this very phrase in assuming responsibility for the blood of Jesus (Mat 27:25). Cf. Mat 23:35.
I am clean (katharos egō). Pure from your blood. Repeats the claim made in previous sentence. Paul had done his duty.
From henceforth (apo tou nun). Turning point reached in Corinth. He will devote himself to the Gentiles, though Jews will be converted there also. Elsewhere as in Ephesus (Act 19:1-10) and in Rome (Act 28:23-28) Paul will preach also to Jews.