# Yahweh will rise up

Yahweh preparing to act is spoken of as if he were sitting and then rising up. 

# Mount Perazim ... Valley of Gibeon

These refer to places where God miraculously defeated enemy armies. 

# he will rouse himself

"he will become very angry"

# his strange work ... his strange deed

This work is strange because God is using a foreign army to defeat the people of Jerusalem rather than helping the people of Jerusalem defeat their enemies.