John XXII (1316-1334) ordered the feast for the entire Church on the first Sunday after Pentecost. A new Office had been made by the Franciscan John Peckham, Canon of Lyons, later Archbishop of Canterbury (d. 1292). The feast ranked as a double of the second class but was raised to the dignity of a primary of the first class, 24 July 1911, by Pius X. The Greeks have no special feast. Since it was after the first great Pentecost that the doctrine of the Trinity was proclaimed to the world, the feast becomingly follows that of Pentecost. (Catholic Encyclopedia)
God so loved the world that he gave his only Son,
John 3:16-18
so that everyone who believes in him might not perish but might have eternal life.
For God did not send his Son into the world to condemn the world, but that the world might be saved through him.
Whoever believes in him will not be condemned,
but whoever does not believe has already been condemned, because he has not believed in the name of the only Son of God.