| “ | We believe in one God, the Father Almighty, Maker of heaven and earth, and of all things visible and invisible. And in one Lord Jesus Christ, the only-begotten Son of God, begotten of the Father before all worlds, Light of Light, very God of very God, begotten, not made, being of one substance with the Father; ... And in the Holy Ghost, the Lord and Giver of life, who proceedeth from the Father, who with the Father and the Son together is worshiped and glorified, who spake by the prophets | „ |
| ~ First Council of Constantinople |
| “ | Because there are three in Heaven that testify—the Father, the Word and the Holy Spirit—and these three are one. | „ |
| ~ — 1 John 5:7 |
The Holy Trinity, commonly known simply as the Trinity, is central to the Christianity.
Theology
One God in three persons
In Trinitarian doctrine, God exists as three persons but is one being, having a single divine nature. The members of the Trinity are co-equal and co-eternal, one in essence, nature, power, action, and will. As stated in the Athanasian Creed, the Father is uncreated, the Son is uncreated, and the Holy Spirit is uncreated, and all three are eternal without beginning. "The Father and the Son and the Holy Spirit" are not names for different parts of God, but one name for God because three persons exist in God as one entity. They cannot be separate from one another. Each person is understood as having the identical essence or nature, not merely similar natures.
According to the Eleventh Council of Toledo (675) "For, when we say: He who is the Father is not the Son, we refer to the distinction of persons; but when we say: the Father is that which the Son is, the Son that which the Father is, and the Holy Spirit that which the Father is and the Son is, this clearly refers to the nature or substance".
The Fourth Lateran Council (1215) adds: "Therefore in God there is only a Trinity, not a quaternity, since each of the three persons is that reality—that is to say substance, essence or divine nature-which alone is the principle of all things, besides which no other principle can be found. This reality neither begets nor is begotten nor proceeds; the Father begets, the Son is begotten and the holy Spirit proceeds. Thus there is a distinction of persons but a unity of nature. Although therefore the Father is one person, the Son another person and the holy Spirit another person, they are not different realities, but rather that which is the Father is the Son and the holy Spirit, altogether the same; thus according to the orthodox and catholic faith they are believed to be consubstantial. "
Clarification of the relationships among the three Trinitarian Persons (divine persons, different from the sense of a "human self") advanced in the Magisterial statement promulgated by the Council of Florence (1431–1449), though its formulation precedes the council: "These three persons are one God and not three gods, for the three are one substance, one essence, one nature, one Godhead, one infinity, one eternity, and everything (in them) is one where there is no opposition of relationship".