In reality everything goes to show that the crumbling away of religious beliefs, which has been going on for the last century and half in vast sectors of the western world, bring as its consequences a weakening of the natural foundation on which these beliefs had grown up. The philosopher, when faced with a fact of such dimensions, is obliged to seek an explanation and to wonder if the principle of these foundations does not contain a certain piety clearly religious in essence. This we might without any offense call sub-Christian, for it is the under structure upon which authentic Christianity is built. It is this understructure, or foundation, which is being destroyed before our eyes to-day, so that the work of reconstruction, of which all recognize the need, has to be carried out, not on the ground level, as in ordinarily imagined, but in an underground region which has to be examined and cleared.
From page 98 of “The Creative Vow as Essence of Fatherhood” in Homo Viator by Gabriel Marcel (1965).