Love seeketh not Itself to please,
 Nor for itself hath any care;
 But for another gives its ease,
 And builds a Heaven in Hell's despair.

     So sang a little Clod of Clay,
     Trodden with the cattle's feet:
     But a pebble of the brook,
     Warbled out these metres meet.

 Love seeketh only Self to please,
 To bind another to Its delight:
 Joys in another's loss of ease,
 And builds a Hell in Heaven's despite.

I’m not sure if by ordering the clod first the poem’s bent is actually pessimistic, but in coming upon this from the pebble’s passion, I found myself rejoyced, and remembered to smile. This is in Songs of Experience, which caught my eye with its illuminated illustrations and pleasant price at a used book sale. Heaven sends the choicest gems to break Hell’s mood!

Your humble Clod,
Gremio

Martin adds

Blake’s ordering of the verses here reminds me of another of his Songs of Experience, “A Poison Tree” [Poem #1087]. It has a similar ‘dark’ structure, upholding (or seeming to uphold) schadenfreude over selflessness. Gremio is right - one would expect the “moral” of the poem to support the clod, and Blake’s letting the pebble have the last word flies in the face of those expectations, making the modern reader (at least) slightly uneasy.