The painting shows St John the Evangelist according to his usual iconography, as a beardless, young man with long hair (to indicate his youthfulness and virginity), wearing a golden tunic and large, red cloak. He is shown genuflecting with a book upon his knee in which he is writing not the Gospel but the Revelation attributed to him, as revealed by his upward-looking gaze. In heaven, two angels hand the woman’s son over to God, depicted by the bust of an old man with pontifical attributes. The woman is shown winged and on her knees with her hands joined about to flee into the desert – the brightness emanating from her body recalls that, according to the text of the Revelation, she is clothed with the sun – and the great battle in heaven is waged by the archangel Gabriel against the great winged serpent with seven heads and seven crowns upon them (Rev. 12: 5-7). Three of the four riders described in the opening of the fourth seal are depicted on earth.
The apostle contemplates a part land, part sky landscape lit not by the sun but by a theophany. Set alongside the evangelist, sitting on the shore of the isle of Patmos – said, according to tradition, to be where he was exiled by Domitian’s government shortly before the year 96 and also, mistakenly, to be where he wrote the Revelation – is his theriomorphic creature, the eagle, with outspread wings. In front of him, an amphibious looking creature – with a long tail, four horns and an open mouth (in reference to physical and moral deviance, applicable only to degenerate, immoral beings) showing its enormous fangs (conveying its fierceness and cruelty) and expelling fire – uses a rod with two hooks at the end (an instrument employed throughout the Middle Ages to seize men’s souls) to steal the inkwell and plume case to prevent him, according to the legend, from writing the Revelation. Visible in the background, in a rocky area of the island are two lions alluding to the wilderness of the setting. Finally, in another reference to the Revelation, on the opposite bank are three of the four riders described in Rev. 6: 1-8. One of the three riders can be identified with the crowned archer, even though he lacks this royal attribute in the illustration and his horse is not white. The second rider, identified with war, bears what seems to be a sword. The final horseman is the most difficult to identify since he should carry a weighing scale in his hands but the instrument he holds aloft cannot be seen clearly in the miniature.