What I dream of is an art of balance, of purity and serenity devoid of troubling or depressing subject matter - a soothing, calming influence on the mind, rather like a good armchair which provides relaxation from physical fatigue.

This quote talks about the kind of art that the speaker would like to find or create. They want art to be balanced and pure, and not to contain anything upsetting or depressing. The idea is that artwork should have a calming effect on the mind; like a comfortable armchair that helps to relieve tension from a tired body.