There's no bodily function as sacred as the sneeze, it seems. It's an act that gets blessed by God left, right and center, sometimes up to four or five times in one snot, uh, shot. Why all the rhinal reverence?
Folklorists believe people began blessing sneezes sometime in the Middle Ages as a way of protecting the soul, which they thought could be ejected violently through the nose every time the unlucky sniffler worked up a good achoo. The blessing acted like a holy safety net in case the devil, always on the prowl for a pious soul to snatch up, was hanging out nearby.
The German gesundheit, literally meaning "good health," is a progressive separation of church and sneeze.