In the writings of John Chrysostom and especially Augustine we find appreciation of nature as a “layman’s Bible,” but it is not until the fifteenth century that this idea becomes widespread. Raymond of Sabunde (c. 1385–1436) was the first thinker to emphasize not only the obvious chronological priority and availability of the book of nature, but also its interpretative clarity in comparison with the book of Scripture. Raymond’s direct influence on Nicholas of Cusa and their conjoint influence on Jan Amos Comenius (1592–1670), the “teacher of nations” and early modern educational and religious reformer, is evident. Less familiar, however, is Comenius’ triadization of the traditional book metaphor. In the sixteenth and seventeenth centuries the two traditional dyads “book of nature–book of Scripture” and “book of the mind–human books” transform into the metaphorical book triad “nature–mind–Scripture.” Such a transformation is slightly suggested already in Augustine and Hugh of St Victor, diffidently expressed in Bonaventure and Cusanus, explicitly postulated in sixteenth-century Lutheran mysticism, and finally impressively developed in Comenius’ universal method of pansophia. Yet while diffident, Cusanus’ development of this theme is nonetheless important. Drawing on the Anselmic, Lullist and “Sabundian” tradition of natural theology, Cusanus as nomenclator Dei seeks God in the maximal Unity that is the same (or “not-other”) with his Triunity. Cusanus’ employment of the book metaphor for both nature and mind prepares the way for Comenius, whose project of universal reform, in the words of Jan Patočka, “suddenly breaks out with a volcanic power from its Cusan germs.” The hypothesis of this chapter is that Comenius’ universal reform included – not as an epiphenomenon but as a conscious and productive intention – the triadic reform of the traditional book metaphor, inspired by Cusan ideas.