Why are D&D PCs resurrectable?
We do not like to think about the metaphysics or theology of D&D settings, so it is generally a question that is left unresolved - and it is not, I think, the subject of much analysis within any particular iteration of the PHB or DMG. (The descriptions of the spells which might resurrect a person - Raise Dead and Resurrection - are entirely about the nuts and bolts of the matter in the 2nd edition version of those books, which are the only ones I have to hand right now.) Various possibilities suggest themselves: when somebody dies his or her soul remains in the body for a certain period of time and the connection between the two can be restored by magic; after death the soul goes into limbo or purgatory or wherever and magic can return it to the body; there is only a cold mechanistic soulless Sam Harris universe and magic can simply reanimate dead flesh; and so on.
One possibility that interests me stems from a recent reading of William Golding's Pincher Martin (spoilers follow, although to be honest the ending is not entirely difficult to see coming). In this book, a British naval officer, who is implied to embody the sin of greed (as well as being a rapist, psychopath, murderer and possibly child molester - it is not a nice book) drowns after having been washed overboard from his ship. But his will proves to be so strong that he creates for himself a sort of afterlife - a rock sticking up from the Atlantic where he can 'survive' and hope to be rescued. In an interesting twist, the rock's shape derives from that of one of his teeth, with whose contours he is of course intimately familiar.
It's safe to say it doesn't end well for him. But I was struck by the concept of a short, time-limited afterlife being the result of an act of will on the part of the dying man or woman - as though human consciousness can linger on in its own reality after the body's death, not through the grace of God but through the refusal on the individual's part to accept dying.
And I was also struck my the nice synergy between this concept and D&D's own, if I can put the matter this way, conceptual priors. Pincher Martin is an existentialist and thoroughly modernist novel in the tradition of Conrad, Melville, Poe, Hemingway - it depicts the human individual as irreducible, human consciousness as atomised and isolated, and the human will as eternally wrestling to create its own values and perhaps even impose them on existence itself. The titular character has his own morality, his own ideals, his own drive, and his own iron will, and at every stage he seeks to force reality to conform.
Golding, a religious man, presents this in a bleak light, but there is no reason why it has to be, and there is something about its anthropology, so to speak, that fits nicely into D&D's own unstated assumptions about the nature of PCs. D&D PCs, at least in the stereotypical 'old school' framework are arch Conradians; while never quite as villainous as Pincher Martin, they are typically paragons of the modernist archetype - autonomous individuals, imbued with their own drives and impulses, with existences that precede essences. They exercise free choice. And because of this there is something appealing about the thought that they possess the ability, like Pincher Martin, to impose their own will on death itself and thereby transcend it - constructing a reality where that will can itself endure until a magic spell can recover it for the world of the living.