Here are some further reflecting on the connections between signs, images, words, language and meaning:
There is nothing inherently more true about an alphabetic text compared to a picture-based text; in some ways the pictures are more 'immediate' because they are less abstracted. If I know nothing at all about iconography or religious symbology, I can still "read" a little bit from mosaics, stained glass or painted icons - from pretty much any geographic area or time period.
A mosaic tile from a baptistry in North Africa from the 300s AD, for example, uses the same symbology as a stained glass window or altar hanging in a 21st century church in Texas (if has these kinds of "decorations.")
I was amazed, walking through a museum in Tunisia, to look up on the wall and, among artifacts from more than a millennium before, see images I clearly recognized as part of my own story now. The oral - or even the written - language of people in Carthage at that time would not be intelligible to me at all, probably. But these images were immediately recognizable; I could read most of them pretty well. There were some symbols I didn't recognize, but most were familiar.
In teaching English to speakers of other languages, I rely heavily on pictures, especially with beginners. Images are more immediate, more universal in that way. Images connect to our sense perception rather than our reason, primarily.
Plato and Aristotle had different views of how we acquire knowledge, or what kind of knowledge is more real, more essential or more true. Platonists generally seem to consider the mind as primary, not the senses. The essential forms of things (which can only be apprehended by reason/contemplation) are more "real" than individual instances of them. Aristotelians, on the other hand, didn't see a need to posit 'forms' which no one could actually see or touch; actual things themselves, then, were more primary.
Platonists (and Western civilization has been more Platonic than Aristotelian since the Enlightenment - that's my theory anyway) focus on knowing things by thinking and abstract reasoning, and words are very good for that, so books have been a big deal.
And, for the same reason, the Protestant Reformation put a big focus on scripture (The WORD) rather than on sacrament (visible expressions of invisible grace, a.k.a. 'transparent signs' - in other words, sensory things like water, bread, wine, oil, icons)
Aristotelians, placing more weight with experience, consider knowledge gained through sense perception to be more primary - so books are not as good for that. Images, sounds, smells, tastes and touch are required for this kind of knowledge. I think this is why folks in the Middle Ages were so keen on categorizing things and sub-categorizing them, and also why they were into illuminating their manuscripts with so much color - and using incense and polyphonic singing and icons and forms of prayer that involved tangibility: prayer beads, walking a labyrinth, going on pilgrimage, etc.
In my opinion, we're swinging back toward a more Aristotelian view, and this is expressed in many aspects of our culture, including the interest expressed in the Internet of compiling all kinds of knowledge and classifying and connecting it and making it all accessible.