There is a great collection of old texts on emblems over at archive.org. A current highlight is the Devises et Emblemes Anciennes & Modernes, Tirees de plus Celoebres Auteurs (1699), which I cannot read a lick of, but has lovely emblems all throughout.
During the Renaissance, the emblem was used to illustrate moral and spiritual truths, often within the context of hermeticism and alchemy. By meditating on the images, a kind of narrative consciousness unfolded. Emblems are particularly important, because they served to emphasize the allegorical nature of these "sciences."
The loss of the emblem in spiritual teachings has in some ways removed the ability to let the symbolic nature of these ideas act on the unconsciousness. We are often presented with ideas as being phenomenal or literal, rather than existing in the nouminous, where the only way to really access them is through these deeper and subconscious kinds of understanding.