What does the line,"art is a reproach to those who receive it"mean?

I would say that inasmuch as art is a commentary on life as we live it and the experiences we have that it can be a reproach if not to the viewer to the broader humanity. For example Picasso's Guernica was a very strong statement against Franco's using the Nazi's to bomb the town of Guernica during the Spanish civil war and his total rejection of fascism.