What is the theme in The Memory Palace of Matteo Ricci by Jonathan D. Spence?

The most obvious theme of The Memory Palace is the idea of the mnemonic device that Matteo Ricci calls the memory palace. A mnemonic device aids in the learning or memorization of some idea or concept. They usually associate a new or unlearned idea with something familiar. Roy G. Biv is one such Mnemonic device, associating the colors of the rainbow with a name that is easy to remember. Matteo Ricci was a master of mnemonic devices, having learned to use them effectively during his years of extensive Jesuit training in Rome and Florence. Ignatius wanted his Jesuit priests to have a vast sum of knowledge, and he also wanted them to memorize important texts. Thus, Ricci needed a method of memorization, and this was one available.