St. Bonaventure said that "The creatures of this sensible world signify the invisible things of God." God is the source, exemplar, and end of every creature; and the Bible and Nature explain each other.
Peachy, but this makes animals nothing more than symbols. Robertsonianism is founded on such principles, that all is understood in terms of Christian allegory for the people of the Middle Ages. Yet that's how the medieval bestiaries work.
An early Greek bestiary, probably the first, originates somewhere between the 2nd and 5th centuries A.D. in Alexandria, seemingly using Egyptian, Greek, Jewish, and Indian sources. This work is attributed to the legendary authority of "Physiologus" (the Naturalist). Was that his name or was the intention to signify Aristotle?
An Old English fragment in the Exeter Book (c. 970-980) has the panther signifying Christ, the whale signifying the devil, and a bird (probably the partridge) signifying God. Anglo-Norman bestiaries proliferate, and a Latin one by an 11th-century monk named Theobaldus of Monte Cassino serves as the main source for the most accessible bestiary to us: the Middle English Bestiarium -- the East Midland text with the difficult dialect, c. 1225-1250. This one is 802 lines treating Theobald's lion (the Lord), eagle (man saved), serpent (shedding sin), ant (work), hart (brotherhood), fox (the devil), spider (betrayal), whale (lure of evil), mermaid (attractive evil), elephant (first fall), turtledove (the spouse of Christ), and panther (Christ). Theobald's centaur is replaced with the culver (another type of dove, also representing Christ).