Just as the Christian has his moments when the clamour of this visible and audible world is so persistent and the whisper of the spiritual world so faint that faith and reason can hardly stick to their guns, as I well remember, the atheist too has his moments of shuddering misgiving, of an all but irresistible suspicion that old tales may after all be true, that something or someone from outside may at any moment break into his neat, explicable, mechanical universe.
Believe in God and you will have
to face hours when it seems obvious
that this material world is the only reality:
disbelieve in Him and you must face hours
when this material world seems to shout
at you that it is not all.
No conviction, religious or irreligious will, of itself, end once and for all this fifth-coumnist [internal subversive agent] in the soul. Only the practice of Faith resulting in the habit of Faith will gradually do that.
–C. S. Lewis
Christian Reflections
Perichoresis 