The Synoptic Gospels
The four gospels are the earliest narrative portraits of Jesus, and were written between, broadly, 65 and 110 CE. They were written for an audience already Christian – their purpose was to strengthen the faith of those who already believed, not to convert unbelievers.
The third creature had the face like man (angel), an evident description of His advent as a human being. St. Irenaeus saw Matthew as corresponding to the man's face because it opens with a human genealogy of Jesus and because, in the view of Irenaeus, Jesus' humanity is emphasized throughout the book.
Christian tradition has long connected the authors of the four canonical Gospels (Matthew, Mark, Luke, John) with the four "living creatures" that surround God's throne, as described in Rev 4:7, in the following pairs:
Matthew = Human/Angel
Mark = Lion
Luke = Ox
John = Eagle
St. Irenaeus stated the first living creature was like a lion symbolizing His effectual working, His leadership, and royal power. This is the symbol of Mark because his Gospel begins with John the Baptist, whose preaching is described as a voice crying in the wilderness like the roar of a lion.
St. Irenaeus indicated the second creature was like a calf or ox, signifying His sacrificial and sacerdotal order. Because Luke opens with a narrative involving priestly duties and temple services, Irenaeus associated it with the only sacrificial animal in the foursome, the ox.