Symbols of the four: —
Matthew. A man with a pen in his hand, and a scroll before him, looking over his left shoulder at an angel. This Gospel was the first, and the angel represents the Being who dictated it.
Matthew a man, because he begins his gospel with the descent of Jesus from the man David.
Mark. A man seated writing, and by his side a couchant winged lion. Mark begins his gospel with the sojourn of Jesus in the wilderness, amidst wild beasts, and the temptation of Satan, “the roaring lion.” (See Lion.)
Luke. A man with a pen, looking in deep thought over a scroll, and near him a cow or ox chewing the cud. The latter part refers to the eclectic character of St. Luke's Gospel.
John. A young man of great delicacy, with an eagle in the background to denote sublimity. The more ancient symbols were—for Matthew, a man's face; for Mark, a lion; for Luke, an ox; and for John, a flying eagle, in allusion to the four living creatures before the throne of God, described in the Book of Revelation: “The first ... was like a lion, and the second ... like a calf, and the third ... had a face as a man, and the fourth ... was like a flying eagle” (iv. 7). Irenæ'us says: “The lion signifies the royalty of Christ; the calf His sacerdotal office; the man's face His incarnation; and the eagle the grace of the Holy Ghost.”.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894