# But you are cast out of your grave

"But you are not buried. Your body is left on the ground" 

# like an abhorrent branch

"like something disgusting that is tossed aside" 

# Those who were killed cover you like a garment

"The bodies of dead people completely cover your body" or "The bodies of dead soldiers are piled on top of your body" 

# those pierced by the sword

"those who were killed in battle" 

# who go down to the stones of the pit

The pit refers either to hell, or to a large hole in the ground where many dead bodies are simply dumped.