Hovering in the early morning sky, a transparent angel appears to absorb and radiate the sun’s rays in Giovanni Bellini’s early Agony in the Garden, which now hangs in the National Gallery in London. Scholars have yet to fully consider the novelty of Bellini’s crystalline angel or angelus cristallum which allows us to consider the artist’s interest in the optical qualities of the materials he represented, especially his fascination with the transparent and lucent effects of crystal, glass, water, and air, and their symbolic value. These optical impressions were governed by the laws of reflection and refraction which late-medieval theologians and natural philosophers sought to explain with their new science of perspectiva. This article explains how Bellini’s Agony, and his angel in particular, indicate his awareness and exploration of this nascent science that connected an understanding of light and vision with a metaphysical exploration of the divine. While discussions of perspective in the Renaissance often center on the development of linear perspective, artists’ interest in capturing the transient effects of light and shadow were wedded to a much broader understanding of perspectiva that included a metaphoric and theological understanding of light. Bellini’s apparent interest in optical principles, especially as they relate to theological issues, suggests a Franciscan context for the painting’s commission, one unrecognized by previous scholars. An exploration of the angelus cristallum and its related metaphors also reveals the extreme naturalism of Bellini’s art and careful layering of religious symbolism. He exposes the power of painting as a means for exploring and knowing the divine and thus provides a richer interpretation of landscape painting avant la lettre.