Matthew 23:27

Woe unto you, scribes and Pharisees, hypocrites! for ye are like whited sepulchres--or, whitewashed sepulchres. (Compare Act 23:3). The process of whitewashing the sepulchres, as LIGHTFOOT says, was performed on a certain day every year, not for ceremonial cleansing, but., as the following words seem rather to imply, to beautify them. which indeed appear beautiful outward, but are within full of dead men's bones, and of all uncleanness--What a powerful way of conveying the charge, that with all their fair show their hearts were full of corruption! (Compare Psa 5:9; Rom 3:13). But our Lord, stripping off the figure, next holds up their iniquity in naked colors. Wherefore ye be witnesses unto yourselves, that ye are the children of them which killed the prophets--that is "ye be witnesses that ye have inherited, and voluntarily served yourselves heirs to, the truth-hating, prophet-killing, spirit of your fathers." Out of pretended respect and honor, they repaired and beautified the sepulchres of the prophets, and with whining hypocrisy said, "If we had been in their days, how differently should we have treated these prophets?" While all the time they were witnesses to themselves that they were the children of them that killed the prophets, convicting themselves daily of as exact a resemblance in spirit and character to the very classes over whose deeds they pretended to mourn, as child to parent. In Luk 11:44 our Lord gives another turn to this figure of a grave: "Ye are as graves which appear not, and the men that walk over them are not aware of them." As one might unconsciously walk over a grave concealed from view, and thus contract ceremonial defilement, so the plausible exterior of the Pharisees kept people from perceiving the pollution they contracted frown coming in…

23:27-28 It was a Jewish custom to coat limestone tombs (perhaps funerary urns or ossuaries) with a mixture of marble and lime to fill their porous surfaces, giving them a more pleasing appearance and helping visitors to Jerusalem to notice the graves and avoid touching them so as not to contaminate themselves. Jesus is not criticizing the adorning of tombs; rather, he points to the similarity between these whitewashed tombs and the teachers of religious law and Pharisees. Both may have looked good on the outside, but both were contaminated and impure within.