The main reason god is invisible is because god probably doesn't exist. The main reason god is *described* as being invisible (more accurately 'transcendental', not just invisible) is because that makes it impossible to test whether or not such an entity exists by empirical means/gives an excuse for the total lack of verifiable evidence. Gods used to be described as physical beings (and there are still remnants of such physical descriptions in most theistic holy books), but when empirical methods began to develop techniques by which such claims could be tested, most of these physical definitions mysteriously evaporated, to be replaced by newly "transcendental" (ie 'conveniently untestable) definitions for 'god. I would never believe in anything based only on the claims of an ancient book. But if any god was visible, or if any verifiable evidence for such a being could be demonstrated, I'd happily accept that such a being exists. Unfortunately no such evidence has ever been demonstrated, despite literally thousands of years of effort by countless individuals. I believe that, since so much effort over such a long time has been utterly unable to provide *any* concrete supporting evidence, it's entirely reasonable to assume that there might be a reason for the lack of evidence. A very, very simple reason, which explains ... well, everything!