The Holy Trinity

See also the section Against Eastern Schismatics

In the Bible

1 John 5:7: “And there are three who give testimony in heaven, the Father, the Word, and the Holy Ghost. And these three are one.”

Matthew 28:19: “Going therefore, teach ye all nations; baptizing them in the name of the Father, and of the Son, and of the Holy Ghost.”

2 Corinthians 13:13: “The grace of our Lord Jesus Christ, and the charity of God, and the communication of the Holy Ghost be with you all. Amen.”

John 14:26: “But the Paraclete, the Holy Ghost, whom the Father will send in my name, he will teach you all things, and bring all things to your mind, whatsoever I shall have said to you.”

Lying to the Holy Ghost is lying to God:

Acts 5:3-4: “But Peter said: Ananias, why hath Satan tempted thy heart, that thou shouldst lie to the Holy Ghost.. Thou hast not lied to men, but to God.”

In Tradition

Pope Eugene IV: “The Holy Roman Church, founded by the voice of our Lord and Savior, firmly believes, professes, and preaches one true God, omnipotent, unchangeable, and eternal, Father, Son, and Holy Ghost… These three persons are one God, and not three gods, because of the three there is one substance, one essence, one nature, one divinity, one immensity, one eternity… It [the Holy Roman Church] condemns, rejects and anathematizes all who think opposed and contrary things, and declares them to be aliens from the Body of Christ, which is the Church.” (Council of Florence, “Cantate Domino,” 1441, ex cathedra)

St. Thomas Aquinas, Summa Contra Gentiles, Book 4, Chap. 14: “… although God the Father is the divine essence, and in the same way God the Son is, from His being the Father He is distinguished from the Son, even though they be one in that each of the two is the divine essence.”

St. Robert Bellarmine on the relations in the Trinity: “Some compare the Father to a fountain, who gives and does not receive; the Son to a river, who receives and gives; the Holy Spirit to a lake, who receives and does not divert the water elsewhere.” (De Christo, Book II, Chap. 27)

Pope St. Leo the Great, Letter 15, July 21, 447: “Besides this one consubstantial, eternal, and unchangeable Godhead of the Most High Trinity there is nothing in all creation which, in its origin, is not created out of nothing.”