There is something both pure and messy about abstract art. On the one hand, one is trying to create something that is beautiful or emotionally resonant in itself, rather that trying to resemble something else (pure art); on the other, there is apparently infinite variety in the way it works (or fails to work) on the viewer.
The relationship with figurative is also complicated. Figurative elements have a way of creeping into abstract pieces, and initially figurative work can become abstract, and be all the better for it.