Two very recondite things befall us in the night. For one thing, the forces of unholiness and spiritual impurity we spoke of scatter about and cover us over then, despite the fact that we’re fast asleep and have nothing to do with it. (Though of course, in general terms, the more worldly and wrongful a person is, the thicker the “blanket” of unholiness overlaying him.)
The other thing is the fact that our immortal souls soar upward to Heaven while we’re sleeping, as we pointed out early on (3:1:6). That obviously doesn’t imply that we die when we sleep (thanks to the fact that our animating spirit is still fully with us then). It’s just to say that we experience a *touch* of death (“a sixtieth” part of it, we’re taught). And so we’re more vulnerable then and open to foul play or even assault by the forces of unholiness. For indeed, for the most part we’re merely bodies, and largely impure ones at that, at night; until we awaken, our immortal souls return, and the forces of G-dliness are reinvigorated in the world.
But a small bit of the night’s precariousness remains behind in the morning, on our fingernails. For something of the noxious spirit that had sat upon our entire person in the night is still there — and only there — after we awake.
So the first element of our daily religious sequence entails what’s referred to as “morning ablutions”, i.e., specific ways of washing our hands ritually; and all in order to remove the night’s impurities.