I would encourage anyone who doubts the potential of visual communication to take a look at the history of the Byzantine Empire. Periods of iconoclasm in the Middle Ages demonstrated how the debate over the proper use of Eastern Orthodox religious material in visual arts exemplified the power of the icon itself. Iconoclasts destroyed visual representations of God, Jesus Christ or the saints. In their view these icons were not just pictorial representations of holy figures but false idols, as people worshiped not to God Himself, but to these painted pieces of wood.
From a design perspective, these Middle-Age icons are incredibly successful at communicating visually (whether they are innately pagan or not) because they imply more than they show. To an Eastern Orthodox worshiper at the time, worshipping to an icon was to implant the power of the Deity or saint in a picture. In my view, this means the painting is working both as an icon and a symbol (that is, it shows the religious figure’s body and at the same time signifies the figure’s spiritual power without depiction).
The iconoclasts had no problem with symbols. They often tore down iconic representations and replaced them with non-pictorial symbols like the cross. To them the symbolic aspect of religious icons was too overwhelmed by the fleshly aspect of depiction.
The fact that an image, be it icon or symbol (or both) can have the power to embody such a complex and significant concept, and exist as an instigator of social strife, testifies to the clout of successful visual communication.