“You are like unmarked graves”
Woe to you! For you are like unmarked graves, which men walk over without even noticing. (Luke 11:44 BSB)
What it sounds like today
Pretty outside, ugly inside: a generic hypocrisy image.
The cultural key
Tombs were freshly whitewashed with lime each spring before Passover for one reason: touching a grave, even unknowingly, brought seven days of corpse impurity (Numbers 19:16) that would disqualify a pilgrim from the feast. The white paint was a warning label: unclean, keep away. Jesus pairs it with the cup washed on the outside while the inside holds 'greed and self-indulgence', glancing at real Pharisaic school debates about whether a vessel's outside could be clean while its inside was not. Luke's image is the exact inverse of Matthew's whitewashed tombs, and it is arguably more damning. The whitewashed tomb at least warns; its paint says 'unclean, keep away.' Luke's grave is unmarked: people walk over it and contract corpse impurity (Numbers 19:16) without ever knowing. Contamination with no warning label at all.
Recovered meaning
The whitewash's whole function is to announce the death inside, so the freshly gleaming facade is the confession. Beauty that exists to manage contact with corruption doesn't hide it; ritually speaking, it labels it.