For it is one thing to adore a picture, another to learn by the story
represented in a picture what is to be adored. For that which the Scriptures
give to those who read them, the picture supplies to those ignorant who behold
it; for in the very image even those who are ignorant see what ought to be
followed, those who cannot read “read” in it. Hence especially for the nations
the picture serves in place of reading. This you, who dwell among the nations,
ought very much to have attended to, lest, while in a right zeal you rashly
blaze forth, you create scandal in fierce minds. Therefore what was placed
there ought not to have been broken, since it was not put in churches for
adoration but only to instruct minds that were ignorant. (Pope Gregory I,
Letter to Secundinus, PL 77:1128 C)
