Much of our understanding of the medieval knowledge of a round Earth actually comes from sermon collections--offhand references to the Earth as a wheel, "the globe of the world," and so on. The point is not that people would learn about the shape of the world from the sermon. Rather, the preacher could throw in such a mention without explication because people were well aware of it.

Now, a necessary warning is that sermons as written are almost certainly not sermons as preached--we have no real way to get from the words on the page to the "speech event" or performance. Indeed, preachers were supposed to use the sermons in collections as a basis to write their own, adding in short illustrative stories (exempla) from separate collections; omitting lengthy passages of citations to various theological stories. On the other hand, we have sources where authors complain that their sermons are being preached word-for-word by uneducated or lazy priests. And the sermon collection known as Dormi secure--"Sleep securely"--takes its name from the promise that preachers can rest easy knowing the sermons they preach from it have been carefully crafted and vetted.