Lyric discussion by mjship11 

Cover art for Crying lyrics by TV on the Radio

“And Mary and David smoke dung in the trenches”

Then “while Zion’s behavior never gets mentioned, the writings on your wall”

I understand the second part. He obviously disagrees with Israel’s policy towards its neighboring countries and the way it is depicted by the media. I also get the allegorical significance of “writing on the wall” which comes from the story in the Bible about Daniel who reads the handwriting on the wall predicting the end of the kingdom of Babylon. Then the “blood on the cradle and the ashes that they wade through” is a reference to the war and destruction in Iraq which is sometimes referred to as the “cradle of civilization”. But what about the first part? What do Mary and David have to do with smoking dung in the trenches?

i think the "And Mary and David smoke dung in the trenches" line refers to Mary the mother of Jesus and David being King David of Israel.

I think this line just talks of how Christians and Jews are sort of in the same trench together facing Muslims in the other trench and they're doing this sh** together (smoking dung) when they shouldn't. My guess is that TVotR are just trying to say how it shouldn't be this religion infused war that it has become.

Good insight. I think you nailed it.