In the Old Testament book of Ezekiel, the prophet has a vision of four living creatures with a human form.
“Within it were figures resembling four living creatures that looked like this: their form was human, but each had four faces and four wings, and their legs went straight down; the soles of their feet were round. They sparkled with a gleam like burnished bronze. Their faces were like this: each of the four had the face of a man, but on the right side was the face of a lion, and on the left side the face of an ox, and finally each had the face of an eagle.” Ezekiel 1:5-10Fire was within the beings, and light shown out from all directions. And their faces looked out in all directions.
Now come with me all the way to the end of the New Testament to the Book of Revelation. Here we have John standing before the throne in heaven and what does he see in the center and around the throne? You guessed it, four living creatures resembling a lion, a calf, a human, and an eagle:
“From the throne came flashes of lightning, rumblings, and peals of thunder. Seven flaming torches burned in front of the throne, which are the seven spirits of God. In front of the throne was something that resembled a sea of glass like crystal. In the center and around the throne, there were four living creatures covered with eyes in front and in back. The first creature resembled a lion, the second was like a calf, the third had a face like that of a human being, and the fourth looked like an eagle in flight. The four living creatures, each of them with six wings, were covered with eyes inside and out. Day and night they do not stop exclaiming: ‘Holy, holy, holy is the Lord God almighty, who was, and who is, and who is to come.’” Rev 4:5-8So it’s not too difficult to see how Tradition has seen these four strange beasts, filled with thunder and fire, shining forth light to all the four corner of the earth, as representations of the four Gospels sharing the same characteristics.
Ok, so if this is where they come from, how do each of the four beasts get tied to each of the Gospels? Well there’s a little disagreement here. Three biggies of the Early Church Fathers: St. Ireneaus, St. Jerome, and St. Augustine didn’t agree. The link from Gospel to symbol is based on what the saint felt the most important aspect of each Gospel was and how it matched with the symbol.
Matthew: Human, Mark: Eagle, Luke: Ox, John: Lion
Matthew: Human, Mark: Lion, Luke: Ox, John: Eagle
Matthew: Lion, Mark: Human, Luke: Ox, John: Eagle
And traditionally, since St. Jerome is seen as alpha-male in all things Biblical, his is the most commonly used.