Although it is difficult to ascribe a particular order to the sections of Books of Hours, the Evangelists (literally “those who announce the gospel or the good news”) frequently appear after the Calendar. The Evangelists serve as an introduction to the Book of Hours, and St. John appears first, followed by St. Luke, St. Matthew, and St. Mark. An illuminated portrait of each saint introduces a brief Gospel Lesson. These lessons, which are extracts from the medieval Missal—the service book used by the clergy—celebrate the Church's four great feasts: Christmas, Annunciation, Epiphany, and Ascension.
Standard iconography represents the Evangelists writing their Gospels, accompanied by their symbol. The illuminations in this case show St. John with his symbol the eagle. Literary texts and the historical interpretation of these texts created the symbolism associated with the Evangelists. In the Apocalypse (Revelation) of St. John a vision of the throne of God contains four living creatures and round about the throne, were four living creatures… And the first living creature was like a lion: and the second living creature like a calf: and the third living creature, having the face, as it were, of a man: and the fourth living creature was like an eagle flying. (The Apocalypse 4:6-7)
St. Jerome applied these symbols to the Evangelists with the following explanations: the human-faced figure represented Matthew, because of Matthew's genealogy of the humanity of Christ; the lion-faced figure represented Mark, because of Mark's mention of the voice of the Baptist in the desert; the ox-faced figure represented Luke, because of Luke's mention of the Jewish priest Zachary; and the eagle-faced figure represented John, because of the soaring flight of John's prologue. (New Catholic Encyclopedia, v. 5, 654).
In some instances, the symbols stand on their own, but more frequently, the symbols accompany its Evangelist. Tools of the trade, the instruments a medieval scribe would have used, appear in the illumination. St. John holds a stylus while the eagle holds an inkwell in his beak. These portraits serve two primary purposes: to present the Evangelists in a recognizable depiction, and to represent the defining characteristic of each Gospel by its symbol (eagle, lion, ox, and winged man).