From the introduction of Jason M. Baxter‘s The Medieval Mind of C.S. Lewis: How Great Books Shaped a Great Mind:

In addition to the Christian apologist, whose sagacious words delivered over radio waves had been so comforting during England’s darkest hour, and in addition to Lewis the mythmaker, the creator of Narnia and fantastic tales of space travel, there was Lewis the scholar, the Oxford (and later Cambridge) don who spent his days lecturing to students on medieval cosmology and his nights looking up old words in dictionaries. This Lewis, as Louis Markos puts it, “was far more a man of the medieval age than he was of our own.” This was the man who read fourteenth-century medieval texts for his spiritual reading, carefully annotation them with pencil; who summed himself up as “chiefly a medievalist” ; the philologist, who wrote essays on semantics, metaphors, etymologies, and textual reception; “the distinguished Oxford don and literary critic who packed lecture theaters with his unscripted reflections on English literature”; the schoolmaster who fussed at students for not looking up treacherous words in their lexicons; the polyglot pedant who did not translate his quotations from medieval French, German, Italian, or ancient Latin and Greek in his scholarly books; the man who wrote letters to children recommending that they study Latin until they reached the point they could read it fluently without a dictionary; the critic who, single-handedly, saved bizarre, lengthy, untranslated ancient books from obscurity.

Baxter M. Jason, The Medieval Mind of C.S. Lewis: How Great Books Shaped a Great Mind. Downers Grove: InterVarsity Press, 2022. (see pages 2,3)

C.S. Lewis cultivated multiple intellectual lives. He was the writer-apologist-professor we remember him as, but in addition, he was a medievalist. Captured by the medieval, his spiritual reading consisted of fourteenth century medieval texts. He gave lectures on medieval cosmology. And there was no need for Lewis to translate texts written in medieval French, German, or Italian. And of course, he possessed a mastery of ancient Latin and Greek.

Also, remember Lewis’ maxim, after reading a new book, never to allow yourself another new one till you have read an old one in between? I mistakenly thought he meant one should re-read a book, before beginning a new one.

Lewis meant read an old book. Like 14th century old, before reading a modern one.