The Four Evangelists [detail of Mark as the Lion]. The Book of Kells. Trinity College, Dublin. ca. 800 AD. Insular script. Gospel of John. The Book of Kells. (Greek kallos/beauty + graphé/writing) an ornamental form of creating letters which involves decorative strokes.

The Book of Kells features a plate depicting the four evangelists in their traditionally symbolic form: Matthew [human/angel], Mark [lion], Luke [ox] and John [eagle]. There are several biblical sources for these symbols, including Ezekiel 1:1-14, Ezekiel 10:1-22, Daniel 7:1-8 and Revelation 4:7-8.

Around the throne, and on each side of the throne, are four living creatures, full of eyes in front and behind: 4:7 the first living creature like a LION, the second living creature like an OX, the third living creature with a face like a HUMAN face, and the fourth living creature like a flying EAGLE. 4:8 And the four living creatures, each of them with six wings, are full of eyes all around and inside.
Revelation 4:7-8

Some scholars believe that Mark was viewed like a son by the disciple Peter and that this chapter of the New Testament most closely reflects Peter's view of the Christ: a servant sent by God to accomplish a specific task. The Gospels of Matthew and Luke use the Gospel of Mark and the Q document as their primary sources.