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-columnist in the soul. Only the practice of Faith resulting in the habit of Faith will gradually do that. I define Faith as the power of continuing to believe what we once honestly thought to be true until cogent reasons for honestly changing our minds are brought before us.