The smallest, first, register, surrounding the lantern, evokes Heavenly Paradise with images of plants and animals including acanthus, facing dolphins, pairs of drinking mammals, birds, and heads in medallions.
Below, in the second register is an image of Christ portrayed as the alpha and omega, beginning and end, described in Rev 1: 17-18.
The open book in his left hand references Col 1:15-16 identifying him as the creator of angels. Thus he is surrounded by nine choirs of angels beginning with seraphim and cherubim to his immediate left and right.