We proclaim Him also by our senses on all sides, and we sanctify the noblest sense, which is that of sight. The image is a memorial, just what words are to a listening ear. What a book is to the literate, that an image is to the illiterate. The image speaks to the sight as words to the ear; it brings us understanding.
St. John Damascene
Apology Against Those Who Decry Holy Images
Part I