Yahweh has accomplished his wrath, he has poured out his fierce anger; He has kindled a fire in Zion, which has devoured the foundations of it.
Lamentations 4:14-15 are difficult passages; but what seems to be the meaning is that death was so widespread in Jerusalem during the siege that the priests were in a constant state of defilement through contact with dead bodies and graves, making them ceremonially unclean, thus robbing the people of any means of religious consolation during their awful desolation.