Trinity Sunday is the feast of the Holy Trinity — the one God in three Persons, Father, Son, and Holy Spirit. It falls on the first Sunday after Pentecost, completing the great arc of the liturgical calendar: the Father sends the Son (Christmas), the Son accomplishes redemption (Easter), the Spirit is given to the Church (Pentecost), and on Trinity Sunday the Church confesses the fullness of God as revealed through these mighty acts. Unlike most feasts, Trinity Sunday commemorates not an event but a doctrine — the central mystery of the Christian faith. The feast is comparatively late in origin. While Trinitarian theology was definitively settled at Nicaea (325) and Constantinople (381), a distinct feast of the Trinity did not become widespread until the medieval period. Individual bishops promoted it — Thomas Becket, consecrated on Trinity Sunday 1162, established it at Canterbury. Pope John XXII made it universal for the Western church in 1334. The BCP tradition, however, gave Trinity Sunday a structural importance beyond Rome's: in the English Prayer Book tradition, the Sundays of the long season after Pentecost are numbered 'after Trinity' rather than 'after Pentecost,' making Trinity Sunday the hinge of the entire second half of the church year. The BCP 2019 lists it among the seven Principal Feasts, and the Athanasian Creed — the most detailed creedal exposition of Trinitarian doctrine — is traditionally appointed for this day.

Trinity Sunday's liturgical tradition reflects the challenge of celebrating a doctrine rather than a narrative. The appointed readings across the three-year lectionary cycle present different facets of Trinitarian revelation: Nicodemus's nighttime conversation with Jesus (John 3), the baptismal commission 'in the name of the Father and of the Son and of the Holy Spirit' (Matthew 28), and Paul's Trinitarian benediction (2 Corinthians 13:14). The Athanasian Creed (Quicunque Vult), with its precise and paradoxical formulations — 'neither confounding the Persons nor dividing the Substance' — has been associated with this feast since at least the ninth century in the West, and the BCP 2019 includes it among its historical documents. The collect for Trinity Sunday is among the most theologically careful in the Prayer Book: 'by the confession of a true faith, to acknowledge the glory of the eternal Trinity, and in the power of your divine Majesty to worship the Unity.' Cranmer's 1549 language echoes here. The white or gold vestments used on this day reflect its status as a feast of the Godhead. In Anglican practice, numbering Sundays 'after Trinity' rather than 'after Pentecost' has given this feast a unique structural role — it names half the church year.

Thomas Ken was born in 1637 at Little Berkhamsted, Hertfordshire, the son of a Protestant gentry family. He attended The King's School, Canterbury, and later Winchester College, then studied at New College, Oxford, where he developed a reputation for theological acumen and piety.

After his ordination, Ken held various church positions, serving as a chaplain and parish minister. In 1679, he became chaplain to Mary of Modena, the Catholic queen of James II, but his unwavering Anglican principles and personal integrity earned him respect even in that delicate position. He refused to compromise the Church's doctrine despite the royal court's proximity to Catholicism.

In 1685, Ken was elevated to the bishopric of Bath and Wells, a position of considerable importance in the English hierarchy. He remained bishop for only three years before the Glorious Revolution of 1688 transformed the English religious and political landscape. When William III and Mary II ascended the throne as joint monarchs, they required all clergy to swear an oath of allegiance to the new sovereigns.

Ken, along with six other bishops, refused to take the oath to William III, maintaining his prior oath to James II as a matter of conscience and principle. This act of non-juror steadfastness cost him his bishopric, his income, and his freedom of movement. He spent his final years in relative poverty and obscurity, first living quietly at Longleat House, then on the Isle of Man (briefly imprisoned), and finally in small rooms in London. He died in 1711, unreconciled to the new regime.

Ken was a skilled theologian and prolific writer of devotional works, sermons, and—most enduringly—hymns. His two hymns, composed in the 1690s, were intended to frame the Christian day: the morning hymn 'Awake my soul and with the sun' and the evening hymn 'All praise to thee my God this night' became canonical in Anglican practice.

Thomas Ken developed no formal cult but became an emblematic figure for the non-juror cause and later for Anglo-Catholic and High Church traditions that valued conscience and principle over mere political pragmatism. His refusal to swear allegiance to William III, despite enormous personal cost, made him a martyr-confessor of principle—suffering not violent death but exile, deprivation, and lifelong poverty for fidelity to his oath. In the nineteenth century, the Oxford Movement and Anglo-Catholic revival recovered his figure as an exemplar of apostolic fidelity and ecclesiastical integrity. However, his commemoration in modern Anglican tradition is primarily through his hymns, which became canonical in Prayer Book services. His hymns frame the Christian day and remain among the most valued in English hymnody. Unlike more overtly hagiographic traditions, Ken's veneration rests on the enduring value of his spiritual compositions and on historical admiration for his conscientious stand, rather than on miraculous claims or a developed cult.