Wake the serpent not

I have no idea what this poetic fragment by Percy Shelley means or where he was going with it. Perhaps the Gentle Reader may have better luck:

Wake the serpent not -- lest he
Should not know the way to go, --
Let him crawl which yet lies sleeping
Through the deep grass of the meadow!
Not a bee shall hear him creeping,
Not a may-fly shall awaken
From its cradling blue-bell shaken,
Not the starlight as he's sliding
Through the grass with silent gliding.