Deep in the heart of man there is a need imprinted by nature that may very well be his basic difference from all other animals: Being a thinking one—i.e., an animal capable of self-awareness—man needs to be something meaningful in his own eyes, something which deserves to exist, possessed of a certain dignity. All men need to give some objective value to their lives.
Each must derive this value either from being an absolute end to himself—which amounts to playing God—or from drawing his personal, and possibly unique, substance not from himself but from playing a meaningful role in some kind of order of which he is only a part, but without which he would remain what a grain of sand is to a desert. Man is an animal longing to belong and to participate.
To satisfy this longing presupposes that man sees the world into which he must fit as something worth existing by itself. His quest for being induces the need for a reason for all things to exist as they are. He cannot help being a religious animal, because he ultimately aspires to having his place in the world—the place, Christians think, God Himself allotted him.
Now, for all men, the world is two-sided: It is a physical entity (each man is part of the natural world), and it is a social entity (no man is an island, unless he is a brute or a god). To achieve his own nature, man must manage to discover what may be his place...