Pain

There's a limit on human tolerance for pain. Pass a breaking point, and the mind shuts down, fainting in some cases, comatose in others, and dead in an unfortunate few- it can't find a home in the in these fried nerve endings. Arguably, this is why we die of old age - a soul refuses to reside in beaten and broken flesh. Entropy wears away like sand on a stone, or disease grips the bones and we are from our one real habitat. But the job of pain isn't to hurt, but to warn of hurt - to call attention to a glitch in the ever renewing and regrowing human body, or to warn of an invasion or terror. And though always uncomfortable, pain may not need feel "bad", we can even get a sense of relief out of pain - like a splinter yearning to be free or a scab pulling on the skin; as C.S. Lewis put it, "It was good pain." Breaking through the hurt is often a vital part of the healign proccess, to the extent that without it, we have no urge to remove the splinter, no matter the infection. Our bodies would no longer have their voice, and they corrode, to be helplessly battered by elements and subject to the gruesome whims we bring them to - until without warnign, they colapse, fail, and ur heart stops, and we are no more.

Truly, the worst thing a Satan could do to the sons and daughters of manking is not hurt, grieve, or even slaughter them; it is numb them until they have no soul left to save.