According to Jewish law, coming into contact with the dead would result in contamination and defilement.  Therefore the Jews were instructed to whitewash, or cover with lime, all tombs and gravesites. Pouring chalk infused water upon the unclean place would make it obvious, and thus easy to avoid.

The practice of yearly whitewashing kept the sepulcher’s facade brilliantly clean and beautiful. Yet, this did not change the true nature of its interior; death and putrefaction.

In an address to the multitudes, Jesus gave instructions to follow the words of the religious leaders, but not the example. He compared their outward signs of piety and honor to the whited veneer of the sepulcher. An attractive appearance can mask internal corruption.

“Even so you outwardly appear righteous to men, but inwardly you are full of hypocrisy and lawlessness.” Matthew 23:28