Master of James IV of Scotland
The Holy Trinity Enthroned
Folio: tempera colors, gold, and ink on parchment
The J. Paul Getty Museum, Los Angeles, California
This page from a breviary or book of hours introduces the morning prayers for Trinity Sunday. God is portrayed above the inscription as three men with three crowns and sceptres but seated on a single throne and identical in appearance. This interplay of three and one reflects the Christian doctrine of the Trinity.
The inscription is on an illiusionistic "scroll" made to seem pinned to the page. The words in red are Die dominica hore de sancta trinitate ad matutinam, "The hours for Trinity Sunday in the morning." The words in black are the customary opening for morning prayers, Domine labia mea aperies, "O Lord, open my lips."
Read more about images of the Trinity.
Source: this page at Wikimedia Commons.