The sculpting of Settignano and Donatello was of an ascension theory that was being paralleled elsewhere differently. Saint Anthony is the parallel of nature to God here for Donatello and you feel like Settignano's understanding of Saint John had a similar residency in the hearts of men. For example, the temptation to experience God with an equation of good and evil was something tenanted with Saint Anthony and Saint John with the feeling of a blessing being needed of Christ and an understanding of God by comparison. The divine creatures of earth are often confused with human sin so people seem to emulate the behaviour of animals through evil rather than deal with their own duty to God and are often not realizing their decent to Hades in doing so or why God wont allow them in heaven. God should be seen in a sheep's back.
Monumento al Gattamelata