The Master of James IV of Scotland visualized the complex Christian doctrine of the Trinity as three crowned figures seated on a throne that hovers in a glowing heavenly light. Each of the three figures is distinct from the waist up but they share one robe, signifying the Christian belief that the Trinity consists of three persons and one substance. In the ethereal space around the throne, transparent angels sing sanctus (Holy). During Church services in the hymn of adoration, sanctus is sung three times, once for each person of the Trinity.
The artist delighted in plays of illusionism. The image's painted frame resembles a carved wooden frame of an altarpiece, suggesting an analogy between an altarpiece and the book. Three lines of text are written on an illusionistically painted slip of parchment, "pinned" to the page of the book to make it appear like a separate piece of parchment. A rubric in red identifies the following text as the prayer for Matins of the Hours of the Holy Trinity, to be read on Sunday. The text, in black ink, begins with a line from Psalm 50: Domine labia mea aperies (Lord, open my lips).