For me, the heaviness of the metal is like the sound of thunder, an avalanche, a howling wind in the winter or the sound of a fall. It's like the sound of the fury of the nature. Sure, it cannot be compared with real nature.
It's a celebration of that side. It can serve us to be humble in face of it.
I think metal music is only really usefull in artificial suroundings like cities. Because who needs metal when we are facing the real deal.