# Your riggings are slack; they cannot hold the mast in place; they cannot spread the sail

Possible meanings: 1) The Assyrian army is like a boat that is unable to move through the water: the ropes that support the mast and sail have come loose and no longer support the mast, so the sail is useless or 2) the people of Judah are no longer at war: "You have loosened the cords that supported your flagpole; the flag no longer flies" 

# mast

tall poles that support the sail

# sail

a large cloth that fills with wind and moves a boat through the water

# the plunder of abundant prey

"the plunder they can take from all of their victims"

# the lame

This refers to people who are cannot walk.