Bugger, missed a bracket !
re: "When the angel woos..."
Angel serves as a metaphor for artists generally (specifically the author) implying a "spiritual" viewpoint. Clay represents non-artists (materialists?), those people with a more "worldly" view.
Translation:
When the artist (angel) pursues material (clay) values he sacrifices the very attributes (wings) which define him.
This is the choice that Kavanagh faces.
AndyG