Artist John La Farge's "Christ Preaching" (1883)—newly returned to the church after a multi-year restoration—is Trinity Church's crowning glory and one of the artist's most significant windows. In 1893 the French critic Samuel Bing (perhaps most famous for coining the term art nouveau) declared that this window's "astonishing brilliance surpasses in its magic anything of its kind in modern times." In this window La Farge combined several of his most innovative features, most notably faceted orbs of blue and green which fill the west wall with an ever-present and glimmering sky. "Christ Preaching" continues to astound observers and is ranked among the finest works in stained glass.

One of the earliest guide books to Trinity notes the instructions Rector Phillips Brooks gave to John La Farge as he undertook the commission: "La Farge, put something there that will be an inspiration to me, as I stand in the pulpit to preach." Indeed, the design elements of the window are closely tied to both Richardson's architecture and Brooks's vision of Trinity as a place of preaching and teaching. Unlike other windows at Trinity, which are given by a specific person or group in honor of an individual's memory, church records note somewhat mysteriously that this window was donated anonymously "by a few parishioners."

While most parishioners today are familiar with the title "Christ in Majesty," "Christ Preaching" is the only title associated with the window in La Farge's time. Where the title "Christ in Majesty" came from is unclear, but seems to date from much later than La Farge's lifetime and took strong hold in the 1970's when people began publishing on La Farge more widely. Expert James Yarnell also notes that after La Farge's death, various sources state that the trumeau sculpture at Amiens inspired the design. However, in 1883 La Farge himself gave his source as drawings by Giovanni Bellini, apparently pulling elements from several works into his final composition.