The text advises artists to develop their own poetic repertoire and highlights Rubens' practice of enriching his imagination through reading. It contrasts Rubens' approach with Leonardo da Vinci's similar methods and explains that the work is not a comprehensive drawing treatise but contains Rubens' reflections on human anatomy influenced by ancient literature. A second volume is mentioned as a supplementary resource focusing on the principles of design applied in practice.
Notice
Other masters had addressed the same subjects. It would be desirable for this repertoire to be in the hands of all artists; however, it would be even better if everyone, according to their style and taste, could create their own poetic repertoire. Rubens understood so well the need for the richest imagination to be nourished by reading, that even while painting, he would have selected pieces of history or poetry read to him.
"Leonardo da Vinci, long before Rubens, made similar extracts, where he drew poetic ideas, subjects of composition, characters, and all the traits of erudition he conveyed in his paintings." Preface to the Urania School, page xvi and following.
Moreover, it is asked that the reader observes that this is not an elementary treatise on drawing, aiming to develop all the principles of this art, but rather reflections by Rubens on the different characteristics of the human body, male and female, inspired by the reading of Virgil, Pliny, and some other ancient authors. To compensate for what this work lacks, a second volume is provided, which serves as a supplement to this one, with the principles of design applied to practice, followed by a large amount of detail.