There are many theoretical ideas behind abstract art. Art for art’s sake - that art should be purely about the creation of beautiful effects is one of the main theories.
Art can or should be like music is another theory. Just as music is made up of patterns of sound, art should be created by pure patterns of form, line and color.
The idea, derived from the ancient Greek philosopher Plato, that the highest form of beauty lies not in the forms of the real world but in geometry, is also used in discussion of abstract art.
As is the idea that abstract art to the extent that it does not represent the material world can be seen to represent the spiritual realm.