Why is the Feast of the Holy Trinity observed after Pentecost?

In Western liturgical churches, the Feast of the Holy Trinity is observed on the Sunday immediately following Pentecost.

Historically, this placement originated in the 10th century when Bishop Stephen of Liège instituted the feast on this specific day. The practice gradually spread throughout northern Europe before being formally accepted for the entire church by Pope John XXII in 1334.12

While the liturgical calendar often uses this feast as a marker—with Anglican and Lutheran traditions dating subsequent Sundays "after Trinity"—the placement itself serves to conclude the festive cycle that begins with Easter and Pentecost. By celebrating the Trinity immediately after the descent of the Holy Spirit at Pentecost, the church emphasizes the fullness of the divine revelation that defines the Christian faith. In contrast, the Eastern Orthodox tradition integrates the celebration of the Trinity directly into the three-day Pentecost feast.12