The Eagle is The Gospel of St. John's Symbol

       "St. John's is preeminently the Gospel for the church, the Gospel of eternity, the spiritual Gospel, the Gospel of Christ as the Eternal Son, and the Incarnate Word." His emblem is the eagle: because "he soars to heaven above the clouds of human infirmity, and reveals to us the mysteries of the God-head, and the felicities of eternal life, gazing on the light of immutable truth with a keen and steady ken."

Scriptural Resources for The Gospel of John's Symbol - An Eagle:

• Jesus said to them, "Truly, truly, I say to you, before Abraham was born, I am." John 8:58
• The crowd then answered Him, "We have heard out of the Law that the Christ is to remain forever; and how can You say, 'The Son of Man must be lifted up'? Who is this Son of Man?" John 12:34
• "The slave does not remain in the house forever; the son does remain forever." John 8:35

St. John's symbol, the eagle, by Rudolf Koch.