"If God exists," many atheists ask us, "why doesn't he make himself present to us?"
Although this question appears reasonable, it is in reality patently absurd, and there are multiple ways to explain this absurdity. Here's just one:
There's a mode of perception proper to every object. Scents are perceived through smelling, music through hearing, food through taste, and so on. All of these can be subsumed into the broader category of objects of sensual perception.
Now, the problem with the above question is that God is a spirit, and, as such, is normally perceived spiritually, not sensually. Why can't most of us perceive him spiritually? Because most of us are spiritually blind (most are not, as Christ puts it, "pure at heart"). But this doesn't disprove God's existence any more than a blind man's inability to perceive a visual object disproves its existence.
In other words, the above question is a loaded one, since it presupposes that God has not made himself present to us. Once we understand that he has, and if we work to sharpen our spiritual perception, we will one day discover that God is indeed "everywhere present and fillest all things," as we recite in the Trisagion Prayers.