John Lightfoot on Matthew 23:29

[Ye garnish the sepulchres of the righteous.] Let them raise some pillar upon his sepulchre. The Glossers are divided about the rendering of the word pillar. Some understand it of a kind of building or pillar; some of the whiting or marking of a sepulchre above spoken of. The place referred to speaks concerning the remains of the didrachms paid for the redemption of the soul: and the question is, if there be any thing of them due, or remaining from the man now dead, what shall be done with it; the answer is, "Let it be laid up till Elias come: but R. Nathan saith, Let them raise some pillar [or building] upon his sepulchre." Which that it was done for the sake of adorning the sepulchres is proved from the words of the Jerusalem Gemara upon the place; They do not adorn the sepulchres of the righteous, for their own sayings are their memorial. Whence those buildings or ornaments that were set on their sepulchres seem to have been sacred to their memory, and thence called as much as souls, because they preserved the life and soul of their memory.

These things being considered, the sense of the words before us doth more clearly appear. Doth it deserve so severe a curse, to adorn the sepulchres of the prophets and righteous men? Was not this rather an act of piety than a crime? But according to their own doctrine, O ye scribes and Pharisees, their own acts and sayings are a sufficient memorial for them. Why do ye not respect, follow, and imitate these? But neglecting and trampling upon these, you persuade yourselves that you have performed piety enough to them, if you bestow some cost in adorning their sepulchres, whose words indeed you despise.