The song writer declared that God is THE Refuge (maḥseh, "shelter from danger") and Strength of believers. In other words they find safety and courage by
trusting in Him, who is always present to help us in times of troubles. So the saints need not fear, even if it evaporates and then an attack comes against them.
The attack language used here is LARGE, to describe how great the perils may be that could come. Earthquakes, waters surge, mountains crumble...get the scope here? No matter what happens, those trusting in Him are safe.
SAFE! Yes you are.