And the temple of God was opened in heaven: and the ark of his testament was visible in his temple, and there were lightnings, and voices, and an earthquake, and great hail.(Apocalypse 11:19)
The illuminator represented the voices as emanating from grotesque featured heads looking down from the edge of the clouds. The roiling earth below suggests the earthquakes that simultaneously strike when Saint John, shielding his eyes, receives his vision of the temple.