In her book The Craft of Thought, Mary Carruthers identifies the purpose of memorization in medieval intellectual culture:
The orator’s “art of memory” was not an art of recitation and reiteration but an art of invention, an art that made it possible for a person to act competently within the “arena” of debate (a favorite commonplace), to respond to interruptions and questions, or to dilate upon the ideas that momentarily occurred to him, without becoming hopelessly distracted, or losing his place in the scheme of his basic speech. That was the elementary good of having an “artificial memory.” …
I repeat: the goal of rhetorical mnemotechnical craft was not to give students a prodigious memory for all the information they might be asked to repeat in an examination, but to give an orator the means and wherewithal to invent his material, both beforehand and — crucially — on the spot. Memoria is most usefully thought of as a compositional art. The arts of memory are among the arts of thinking, especially involved with fostering the qualities we now revere as “imagination” and “creativity.”
Today people will tell you that memorization is the enemy of creativity; these medieval thinkers understood that precisely the opposite is true: the more you have memorized the greater will be your powers of invention.