Ye be witnesses unto yourselves - The emphasis, here, lies in the words “to yourselves.” It is an appeal to their conscience. It was not by their building the tombs that they were witnesses that they were the children of those who killed the prophets; but that, in spite of all this pretence of piety, under all this cloak of profession, they knew in their consciences, and were witnesses to themselves, that it was mere hypocrisy, and that they really approved the conduct of those who slew the prophets.
Children of them ... - Resembling them; approving their conduct; inheriting their feelings. See the notes at Matthew 1:1. They not only showed that they were descended from them, but that they possessed their spirit, and that, in similar circumstances, they would have done as they did.