The lefthand page uses a very large capital “B” to enclose a scene of the monk and abbott having their conversation. The text will be shaped around the box. My favorite source for this book (and  Come to the Castle) is the Luttrell  psaltery. The artist for that book employed a design where the left hand side of the page has a decorative vertical banner that is connected to the big decorated first letters of the paragraphs. The banner often has horizontal branches of leaves and fanciful items. These form a border around three sides, almost enclosing the text block. The righthand page here uses that design with the borders enclosing a scene and text.