The high priest is my witness — Is able to testify. The brethren — Jews: so this title was not peculiar to the Christians.
Related Commentaries of Acts 22:5
Acts 22:5
5 As also the high priest doth bear me witness, and all the estate of the elders: from whom also I received letters unto the brethren, and went to Damascus, to bring them which were there bound unto Jerusalem, for to be punished.