Robert captains a seriously deep episode on the father of Scholasticism, Doctor of the Church Thomas Aquinas. Francis is in awe and Martin works hard to keep up. 

Reading much of Thomas Aquinas is a magnum opus unto itself, but his great masterwork, the Summa Theologica (often just called the Summa) is available online for free and in its entirety on the New Advent website.

And believe it or not, his Wikipedia page does a very good free biography of him and of his many great contributions to learning.