The Invisible Man is about a guy with no friends, no family, and, well, just no one at all. It seems like no matter where he finds himself, he's isolated from the larger community – he's as alone in Iping as he is in London. If the Invisible Man were just a hermit who lived alone by choice, that would be one thing. But our guy is a genius scientist who is surrounded by people; they just don't understand him. That might be the worst form of isolation: surrounded by people but always alone. And it's worth mentioning that some critics think that science becomes dangerous when it's isolated from the larger community; if we think of Griffin as a symbol for science-gone-wrong, this makes a lot of sense.
The Invisible Man shows us that a person will become a monster when isolated from the rest of humanity.
Griffin is the cause of his own isolation. If he reached out to other people, he wouldn't be in the same position.