John Gill

And now, brethren,.... He calls them brethren, because they were so according to the flesh; and to testify his cordial love and affection for them. I wot, or "I know", that through ignorance ye did it; delivered up Jesus into the hands of Pilate; denied him to be the Messiah before him; preferred a murderer to him, and put him to death. As did also your rulers; the members of the sanhedrim, some of them; see Co1 2:8 for others of them knew him to be the Messiah, to be sent of God, by the miracles he did, and yet blasphemously ascribed them to Satan; and so sinning against light and knowledge, in such a malicious manner, sinned the sin against the Holy Ghost, to which ignorance is here opposed; and which did not excuse from sin: nor was it itself without sin; nor is it opposed to any sin, but to this now mentioned.