On the front of the house I have a meter and below it is a sub panel. I open the cover and there is a single switch in the middle of the panel (looks like a giant light switch) and it is spring loaded. You cannot turn it off. Can you tell me what is the purpose and how to turn off?
From the description, not a sub-panel, but a main disconnect switch.
Unclear why you are having trouble switching it off - if having trouble switching it ON, you might have a problem causing it to trip (they are almost always circuit breakers, not "merely switches")
It probably will take considerable force to switch off, but you should not need (nor use) a prybar or hammer on it. ;-) A forceful and determined motion of the hand towards the "off" direction should suffice.