This is from Eric Voegelin's lecture "In Search of the Ground".
One should be aware that we always act as if we had an ultimate purpose in fact, as if our life made some sort of sense. I find students frequently are flabbergasted, especially those who are agnostics, when I tell them that they all act, whether agnostics or not, as if they were immortal! Only under the assumption of immortality, of a fulfillment beyond life, is the seriousness of action intelligible that they actually put into their work and that has a fulfillment nowhere in this life however long they may live. They all act as if their lives made sense immortally, even if they deny immortality, deny the existence of a psyche, deny the existence of a Divinity—in brief, if they are just the sort of fairly corrupt average agnostics that you find among college students today. One shouldn’t take their agnosticism too seriously, because in fact they act as if they were not agnostics!