Feast of the Holy Trinity

The Catholic Church celebrates this unfathomable mystery each year on the Sunday following Pentecost.

What is Holy Trinity Sunday?
The Catechism of the Catholic Church (paragraph 234) teaches:
The mystery of the Most Holy Trinity is the central mystery of Christian faith and life. It is the mystery of God in Himself. It is therefore the source of all the other mysteries of faith, the light that enlightens them. It is the most fundamental and essential teaching in the “hierarchy of the truths of faith.” The whole history of salvation is identical with the history of the way and the means by which the one true God, Father, Son and Holy Spirit, reveals himself to men “and reconciles and unites with himself those who turn away from sin.”

What does it mean for the Trinity to be a Mystery?

The objects of the Christian Faith, such as the Trinity, are above created natures. As supernatural realities, they cannot be discovered by reason or the senses, but must be revealed by God, who alone fully knows and understands them. This makes the Trinity a mystery.

Even so, we can reason about the mysteries of the Faith by analogy to the things that we do know, showing that they are not incompatible with reason, just beyond its natural comprehension. This possibility is the basis of the various dogmas regarding the mysteries of the Faith which the Church has promulgated over the centuries, as well as of the reasoned conclusions of theologians—all founded upon the act of Faith in the truth of the mystery.

Who are the three Divine Persons of the Blessed Trinity?

God the Father, God the Son, and God the Holy Spirit are the Three Divine Persons of the Blessed Trinity.

Father

God the Father is the First Person of the Blessed Trinity. This means He is the Source or Principle of what is call the “processions” of the other two Persons.

In the Old Testament references to “God,” whether Yahweh, or Adonai, or by other Names are references to the Divine Nature, but in some sense are also to the “principle” of that Nature, the Father, from Whom the Godhead proceeds eternally. Thus, the Christian can take references to God in Scripture to be to the Unity of the Divine Nature or to the Father, depending on context.

Son

The Son is the Second Person of the Blessed Trinity. He proceeds from the Father as His Divine Word from all eternity. The term “generation” is also used for this procession. The human analogy of Sonship, therefore, reflects this, and the fact that the Second Person is the Word of God, or the image as St. Paul explains (Colossians 1:15).

Holy Spirit

The Holy Spirit is the Third Person of the Blessed Trinity. He proceeds from the Father and the Son as their Spirit, the Spirit of Love.

Where did the term Trinity originate?

In Scripture it is revealed that God is One and God is Three, in that the Father is God, the Son is God, and the Holy Spirit is God. This faith was held by the Church from her beginning. With time a theological language was developed, largely to exclude various errors about the nature of God (e.g. three gods, or three modes or aspects of God). After the end of Roman persecution in 313 A.D., the theological work of defeating errors regarding God and Christ would occupy the Church through her great Councils of the 4th and 5th centuries.

Trinity, specifically, seems to have been in use by the end of the second century. It is found as the Greek trias around 180 A.D.—in Theophilus of Antioch, who explains, “the Trias of God [the Father], His Word and His Wisdom (“Ad. Autol.”, II, 15). Tertullian would adopt the Latin Trinitas, and the term would become common in the third century.

“In all our actions, when we come in or go out, when we dress, when we wash, at our meals, before retiring to sleep, we make on our foreheads the sign of the cross.” – Tertullian (c.200 A.D.)

What does it mean for God to be a “Trinity”?

The Catechism (paragraphs 253-255) further explains, stating,
The Trinity is One. We do not confess three Gods, but one God in three persons, the “consubstantial Trinity.” The divine persons do not share the one divinity among themselves but each of them is God whole and entire: “The Father is that which the Son is, the Son that which the Father is, the Father and the Son that which the Holy Spirit is, i.e. by nature one God.” In the words of the Fourth Lateran Council of 1215, “Each of the persons is that supreme reality, viz., the divine substance, essence or nature.”

The divine persons are really distinct from one another. “God is one but not solitary.” ”Father”, “Son”, “Holy Spirit” are not simply names designating modalities of the divine being, for they are really distinct from one another: “He is not the Father who is the Son, nor is the Son he who is the Father, nor is the Holy Spirit he who is the Father or the Son.” They are distinct from one another in their relations of origin: “It is the Father who generates, the Son who is begotten, and the Holy Spirit who proceeds.” The divine Unity is Triune.

The divine persons are relative to one another. Because it does not divide the divine unity, the real distinction of the persons from one another resides solely in the relationships which relate them to one another: “In the relational names of the persons the Father is related to the Son, the Son to the Father, and the Holy Spirit to both. While they are called three persons in view of their relations, we believe in one nature or substance.” Indeed “everything (in them) is one where there is no opposition of relationship.” “Because of that unity the Father is wholly in the Son and wholly in the Holy Spirit; the Son is wholly in the Father and wholly in the Holy Spirit; the Holy Spirit is wholly in the Father and wholly in the Son.”

“A Christian receives divine wisdom in three ways: by the commandments, teachings, and faith. The commandments free the mind from passions. Teachings lead it to true knowledge of nature. Faith leads to the contemplation of the Holy Trinity.” – St. Maximus the Confessor (c.650)

 
*Reference EWTN