I thought this was a bittersweet, sad story. The emotions of the characters: pain, loss, loneliness and hopelessness, are, as we all know, human emotions, too.
The story had themes of change throughout. The androids are making themselves appear less human. The Angel makes himself in the image of the Android's lost lover, and the angels turn into water. In the end, the Android is wanting to turn into stone.
Humans (in real life, and in the story's past) change ourselves. Whether we want to mimic others, change our appearance to please someone else, or make our outsides look like who we really are on the inside.
- J.K. Parsons