Pope Gregory, as quoted in the St Albans Psalter:
It is one thing to worship a picture; another to learn, through the story of a picture, what is to be worshipped. For the thing that writing conveys to those who read, that is what a picture shows to the illiterate; in the picture itself those who are ignorant see what they ought to follow. In [the picture] itself those who are unacquainted with letters [are able to] read. Whence, and particularly among common folk, a picture serves in place of reading.
But we walk by faith, not by sight, and faith comes by hearing. Both those who can read, who look at letters, and those who can’t read, who look at pictures – oversimplifications here, mind you! – have the benefit of hearing the Word read and preached. The oral word is the primary source; the visual representation, whether in letters or in iconography, is secondary. Ad fontes, ad fontes.
The Word became flesh. The focal point of seeing, where there is one, is the fruit of the Tree of Life, the fulness of the Cross, the Eucharist of which we can sing:
Lord, now lettest thou thy servant depart in peace :
according to thy word.
For mine eyes have seen :
Which thou hast prepared :
before the face of all people;
To be a light to lighten the Gentiles :
and to be the glory of thy people Israel.
All seeing flows from thence, and all visual representation.