These are coded mnemonic images used to recall specific passages of the gospels based on the symbolic images of the four evangelists, Matthew, Mark, Luke, and John. The symbols of the evangelists are derived from the Old Testament visions of Ezekiel and the vision of St. John in The Apocalypse. In the West, the beasts of St. John's vision are usually associated with the evangelists as follows: Matthew is represented by a man; Mark by the lion; Luke by the bull; and John by the eagle. These symbols often appear alone, in iconography and illuminated manuscripts, either with attributes such as wings, halos, and books, or without. They sometimes accompany portraits of the evangelists, or they are sometimes conflated with human figures to form anthropomorphic symbols.
These four animal/evangelist symbols will be familiar to students of Tarot iconography, where they are also associated with the four elements, cardinal directions, and astrological signs; Matthew = Man = Aquarius = Air = East; Mark = Lion = Leo = Fire = South; Luke = Bull = Earth = Taurus = North; John = Eagle = Scorpio = Water = West. These are typically pictured in the corners of the XXI Trump "Le Monde" or "The World" framing the Vescica Piscis, Mandorla, or Almond-shaped wreath framing in turn the figure of Christ (in early Marseille Tarots), or the Virgin (Anima Mundi).
Elsewhere Henri Bouchot and Anton Einsle write:
The Ars Memoranda, another xylographic work, of which the subject, taken from the New Testament, was equally well adapted to the imagination of the artists, had an equally glorious destiny. The work originally comprised thirty blocks, the fifteen blocks of text facing the fifteen engravings. The designs represented the attributes of each of the Evangelists, with allegories and explanatory legends. Thus, in that which relates to the Apostle Matthew:
#1 represents the Birth and Genealogy of Jesus Christ
#2 the Adoration of the Magi
#3 the Baptism of St. John
#4 the Temptation of Christ
#5 the Sermon on the Mount
#6 the Parable of the Birds
The angel that supports the whole is the emblem of St. Matthew the Evangelist.