Jewish people used to coat limestone tombs, like funerary urns or ossuaries, with a mixture of marble and lime. This filled the holes and made the tombs look nicer. It also helped visitors to Jerusalem see and avoid them, preventing contamination. Jesus did not criticize decorating tombs. Instead, he compared these whitewashed tombs to Jewish religious teachers and Pharisees. Both looked good on the outside but had contamination and impurity on the inside.