Holy Trinity Sunday is celebrated on the first Sunday following Pentecost in most of the liturgical churches in Western Christianity. It is a solemn celebration of the belief in the revelation of one God, yet three divine persons. It was not uniquely celebrated in the early church, but as with many things the advent of new, sometime heretical, thinking often gives the Church a moment in which to explain and celebrate its own traditions; things it already believes and holds dear. In the early 4th century when the Arian heresy was spreading, the early church, recognizing the inherent Christological and Trinitarian implications, prepared an Office of Prayer with canticles, responses, a preface, and hymns, to be recited on Sundays to proclaim the Holy Trinity. Pope John XXII (14th century) instituted the celebration for the entire Church as a feast; the celebration became a solemnity after the liturgical reforms of Vatican II. Continue reading
Trinity Sunday: context
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All power…all nations… all that I have commanded you…with you always – One should be struck by the repetition of the word “all” in this passage:
Commentary – Jesus was from Galilee and since the beginning of his public ministry had moved from the northern most reaches of Israel to its center in Jerusalem – the locus of the confrontation and rejection by the leaders of Israel. But now the “Galilean” has triumphed against all odds and it a manner none had foreseen. The preparation of the “twelve” was not lost in their abandoning Jesus at the Passion. They are now restored to their positions of trust and responsibility and given final instructions for fulfilling the mission to which they had already been called (cf. 10:1-15) – but the scope is now far wider than Israel and included all the nations (28:19) 
Matthew 28:16-20 16 The eleven disciples went to Galilee, to the mountain to which Jesus had ordered them. 17 When they saw him, they worshiped, but they doubted. 18 Then Jesus approached and said to them, “All power in heaven and on earth has been given to me. 19 Go, therefore, and make disciples of all nations, baptizing them in the name of the Father, and of the Son, and of the holy Spirit, 20 teaching them to observe all that I have commanded you. And behold, I am with you always, until the end of the age.” 
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