Our predecessor Innocent XII, absolutely refused the petition of those who desired a special festival in honour of God the Father. For, although the separate mysteries connected with the Incarnate Word are celebrated on certain fixed days, yet there is no special feast on which the Word is honoured according to His Divine Nature alone. And even the Feast of Pentecost was instituted in the earliest times, not simply to honour the Holy Ghost in Himself, but to commemorate His coming, or His external mission. And all this has been wisely ordained, lest from distinguishing the Persons men should be led to distinguish the Divine Essence. Moreover the Church, in order to preserve in her children the purity of faith, instituted the Feast of the Most Holy Trinity, which John XXII. afterwards extended to the Universal Church. He also permitted altars and churches to be dedicated to the Blessed Trinity, and, with the divine approval, sanctioned the Order for the Ransom of Captives, which is specially devoted to the Blessed Trinity and bears Its name. Many facts confirm its truths. The worship paid to the saints and angels, to the Mother of God, and to Christ Himself, finally redounds to the honour of the Blessed Trinity. In prayers addressed to one Person, there is also mention of the others; in the litanies after the individual Persons have been separately invoked, a common invocation of all is added: all psalms and hymns conclude with the doxology to the Father, Son, and Holy Ghost; blessings, sacred rites, and sacraments are either accompanied or concluded by the invocation of the Blessed Trinity. This was already foreshadowed by the Apostle in those words: "For of Him, and by Him, and in Him, are all things: to Him be glory for ever" (Rom. xi., 36), thereby signifying both the Trinity of Persons and the Unity of Nature: for as this is one and the same in each of the Persons, so to each is equally owing supreme glory, as to one and the same God.
Leo XIII, Divinum Illud Munus, 3.