Trinity Sunday honours the Holy Trinity. It is dedicated to the doctrine of the Holy Trinity, the essence of God expressing itself in three persons: God the Father, Jesus Christ and Holy Spirit. Trinity Sunday serves as a reminder for all the Holy Trinity has done to salvage humanity from its sins.
Theologically, the Trinity is a common thread among most Christians faiths. Trinity Sunday falls on the first Sunday after Pentecost in the Western churches while in the Eastern churches, Pentecost Sunday itself is Trinity Sunday.
Trinity Sunday was established by Pope Gregory IX in the 9th century. However, it has been celebrated as a tradition for hundreds of years before 828 CE as indicated in the adoption of the Trinitarian baptismal formula in early liturgies at the local level by churches and dioceses. Trinity Sunday was established as a feast day by Pope John XXII in 1334. Since then, Trinity Sunday is universally observed by all Christians in Western Churches., which include Roman Catholic, Anglican Lutheran, Presbyterian, United Church of Christ and Methodist.