When I reflect on the symbols of each, I see a differing connection, than does St. Jerome, as many of The Saints and writers above, mentioned.
St. Matthew, I see, is the Lion. His Gospel was written to the Hebrews, and details the connection of Jesus as Messiah, described in the Old Testament Prophecies. The symbol of Judah is a Lion. The Lion protects and cares for His own As such, He is a guardian. Jesus fulfills the Messianic Lineage which was seen as significant as an Old Covenant Witness.
St. Mark is the Ox. The Ox is a symbol of power, as appropriate since Mark’s Gospel was written to the Roman. St. Mark presents The Lord as a Revolutionary. He plows through the Establishment asserting His own authority, and setting up the Divine Kingdom of Heaven in The Church over a rebellious world.
St. Luke is the Man. Contemplative and detailed. St. Luke is a beloved Physician (Colossians 4:14) writing His Gospel to a fellow Greek. (Luke 1:1-3; Acts 1:1) Luke’s lineage of Jesus takes him back 77 Generations before Adam to God. (Luke 3) Jesus became Man and is expressed by Luke as a Servant. Our Salvation rests ultimately in our humility, exemplified in Christ. (Philippians 2:5-11)
St. John is the Eagle. A Witness to All People who believe so that we may have Life in His Name (John 20:30-31; 21:24-25) He is The Lamb of God who takes away The Sins of the world (John 1:29; 35) proclaiming the everlasting Gospel (John 1:11-13) to all nations. (John 14:6)
Interestingly, each creature is identified in that order. 1st, the Lion, 2nd, the Ox, 3rd, the Man, 4th, the Eagle (Revelation 4:6-8) which parallels Matthew, Mark, Luke and John. Christ comes through the Tribal Vessel as Messiah, and the Larger picture of His role as 2nd Adam (1 Corinthians 15:45-49) and Redeemer of all who believe (John 3:16-17) are gradually revealed. There are crossovers in substance for Each Gospel, because ultimately the 4 Gospels are a single Gospel Witness of Christ’s Mediation between Man and God. (1 Timothy 2:4-5)