Yahweh continues to speak of the false security that the prophets have given to the people by speaking of peace as if the prophets had built a poorly-constructed wall and covered it over with white paint in order to make it look good. (See: [[rc://en/ta/man/translate/figs-metaphor]])
The word "whitewash" refers to a white liquid mixture or paint used to cover up impurities and make surfaces white. See how you translated this in [Ezekiel 13:10](../13/10.md).