Trinity Sunday is celebrated on the first Sunday after Pentecost. It initiates the celebration of a doctrine instead of an event. It is also symbolic of the unity of the Trinity. Trinity begins eight weeks after Easter and continues for about half of the calendar year.
Background: Pope Gregory IX instituted Trinity Sunday in 828 CE. This day is notable for being the only major Christian festival that celebrates a doctrine of the church rather than an event in its sacred history. It is dedicated to the Christian belief in the Trinity – Father, Son and Holy Spirit – and falls on the Sunday following Pentecost each year. The belief of one God in three elements is distinctive of the Christian faith.
Constantine the Great, the first Christian emperor, in A.D. 325 asked the bishops from the entire church to come together at Nicaea to discuss and agree on a creed for the complex nature of the Trinity. What is called the Nicene Creed was completed in 381.
Beginning with Augustine in the fifth century, attempts have been made to provide analogies from our human experiences to shed light on the doctrine of the Trinity. For instance, Augustine extracted a clear comparison from botany: “The root is wood, the trunk is wood, and the branches are wood, while nevertheless it is not three woods that are thus spoken of, but only one…. [Thus] no one should think it absurd that we should call the Father God, the Son God, the Holy Spirit God, and that these are not three gods in the Trinity, but one God and one substance.”
There is a profound complexity in the orthodox Christian doctrine of God, but it is not incomprehensible. Although humans do not have a full understanding of God, there is a reasonable basis for belief in the triune God. The doctrine expresses genuine monotheism.
The Shamrock and the Trinity:Legend has it that when Saint Patrick told the King of Ireland about the Trinity, the king could not believe three Persons in the Godhead could exist as one. Lifting up a sprig of shamrock, Saint Patrick said: “Here is a perfect leaf with three perfect parts.” The shamrock became a well-known symbol of the Holy Trinity.
