>Thanks for the reference.
Baxandall's book is great. I think Chuck would like him because he spent lots of time at the Warburg Institute. I think he taught at Berkeley too. Here's one source he was working from in Painting and Experience.
From Catholicon by John of Genoa, (13th century):
You have to understand there are three reasons for paintings in churches. First, for educating simple people, because the painting teaches them as a book would. Second, the mysteries of embodiment and the appearance of the saints are more active in our minds if we look at them every day. Third, they encourage religious feelings, for they are more in touch with the visual image, than with the spoken word.