Luke 11:20
The third woe — you are like unmarked graves, which people walk over without knowing it — identifies the Pharisees as sources of invisible defilement: they appear as religious guides but lead people into death-contact they do not recognize. Numbers 19:16 specified that contact with a grave defiled; the unmarked grave defiled the unwary traveler. The Pharisees are the unmarked spiritual graves of their generation.