instance. The meanings accruing to the symbols grew over centuries, with an early formulation by Jerome, and were fully expressed by Rabanus Maurus, who set out three layers of meaning for the beasts, as representing firstly the Evangelists, secondly the nature of Christ, and thirdly the virtues required of a Christian for salvation: These animals may have originally been seen as representing the highest forms of the various types of animals, i.e., man, the king of creation as the image of the creator; the lion as the king of beasts of prey (meat-eating); the ox as the king of domesticated animals (grass-eating) and the eagle as the king of the birds. Matthew the Evangelist, the author of the first gospel account, is symbolized by a winged man, or angel. Matthew's gospel starts with Joseph's genealogy from Abraham; it represents Jesus' Incarnation, and so Christ's human nature. This signifies that Christians should use their reason for salvation. Mark the Evangelist, the author of the second gospel account, is symbolized by a winged lion – a figure of courage and monarchy. The lion also represents Jesus' resurrection (because lions were believed to sleep with open eyes, a comparison with Christ in the tomb), and Christ as king. This signifies that Christians should be courageous on the path of salvation. Luke the Evangelist, the author of the third gospel account (and the Acts of the Apostles), is symbolized by a winged ox or bull – a figure of sacrifice, service, and strength. Luke's account begins with the duties of Zechariah in the temple; it represents Jesus's sacrifice in His Passion and Crucifixion, as well as Christ being High priest (this also represents Mary's obedience). The ox signifies that Christians should be prepared to sacrifice themselves in following Christ. John the Evangelist, the author of the fourth gospel account, is symbolized by an eagle – a figure of the sky, and believed by Christian scholars to be able to look straight into the sun. John starts with an eternal overview of Jesus the Logos and goes on to describe many things with a "higher" christology than the other three (synoptic) gospels; it represents Jesus's Ascension and Christ's divine nature. This symbolizes that Christians should look on eternity without flinching as they journey towards their goal of union with God. Each of the symbols is depicted with wings, following the biblical sources first in Ezekiel