Matthew 23:29-31

Verse 29. Ye build the tombs of the prophets. That is, ye build sepulchres or tombs over the prophets that have been slain. This they did professedly from veneration, and respect for their character. This is often done in the East at the present day, and indeed elsewhere. Among the Mohammedans it is a common way of showing respect for any distinguished man to build a tomb for him. By doing this they profess respect for his character, and veneration for his memory. So the Pharisees, by building tombs in this manner, professedly approved of the character and conduct of the prophets, and disapproved of the conduct of their fathers in killing them.

And garnish, etc. That is, adorn or ornament. This was done by rebuilding them with more taste, decorating them, and keeping them neat and clean. The original word means, also, to show any proper honour to the memory of the dead; as by speaking well of them, praying near them, or rearing synagogues near to them, in honour of their memory.
Verse 30. And say, etc. This they professed to say by rebuilding their tombs. They also, probably, publicly expressed their disapprobation of the conduct of their fathers. All this, in building and ornamenting tombs, was a profession of extraordinary piety. Our Lord showed them it was a mere pretence. Verse 31. Ye be witnesses unto yourselves. The emphasis, here, lies in the words "unto yourselves." It was 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 slew the prophets; but in spite of all this pretence to piety--under cloak of all this 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, etc. Resembling them; approving their conduct; inheriting their feelings. They not only showed that they were descended from them, but that they possessed their spirit, and in similar circumstances would have done as they did.

(n) "which killed" Acts 7:52, 1Thes 2:15
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