What does this mean?: Caedite eos! Nobit enim Dominus qui sunt eius?

Question

It's on the back of the Five Finger Death Punch shirt and I want to know what it means?

Answer 1

Well, I know it's Latin.  Is that worth 2 pts?

Answer 2

Caedite eos. Novit enim Dominus qui sunt eius.

it is usually translated:

Kill them all! God will recognise his own.

But you need to know the story to understand it.