200 These are the words with which the Niceno-Constantinopolitan Creed begins. the confession of God's oneness, which has its roots in the divine revelation of the Old Covenant, is inseparable from the profession of God's existence and is equally fundamental. God is unique; there is only one God: "The Christian faith confesses that God is one in nature, substance and essence." [Roman Catechism I, 2, 2.]

201 To Israel, his chosen, God revealed himself as the only One: "Hear, O Israel: the LORD our God is one LORD; and you shall love the LORD your God with all your heart, and with all your soul, and with all your might." [Dt 6:45.] Through the prophets, God calls Israel and all nations to turn to him, the one and only God: "Turn to me and be saved, all the ends of the earth! For I am God, and there is no other.. . To me every knee shall bow, every tongue shall swear. 'Only in the LORD, it shall be said of me, are righteousness and strength.'" [Is 45:22-24; cf. Phil 2:10-11.]

202 Jesus himself affirms that God is "the one Lord" whom you must love "with all your heart, and with all your soul, and with all your mind, and with all your strength". [Mk 12:29-30.] At the same time Jesus gives us to understand that he himself is "the Lord". [Cf. Mk 12:35-37.] To confess that Jesus is Lord is distinctive of Christian faith. This is not contrary to belief in the One God. Nor does believing in the Holy Spirit as "Lord and giver of life" introduce any division into the One God:

233 Christians are baptized in the name of the Father and of the Son and of the Holy Spirit: not in their names, [Cf. Profession of faith of Pope Vigilius I (552): DS 415.] for there is only one God, the almighty Father, his only Son and the Holy Spirit: the Most Holy Trinity.

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253 The Trinity is One. We do not confess three Gods, but one God in three persons, the "consubstantial Trinity". [Council of Constantinople II (553): DS 421.] 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." [Council of Toledo XI (675): DS 530:26.] In the words of the Fourth Lateran Council (1215), "Each of the persons is that supreme reality, viz., the divine substance, essence or nature." [Lateran Council IV (1215): DS 804.]

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258 The whole divine economy is the common work of the three divine persons. For as the Trinity has only one and the same natures so too does it have only one and the same operation: "The Father, the Son and the Holy Spirit are not three principles of creation but one principle." [Council of Florence (1442): DS 1331; cf. Council of Constantinople II (553): DS 421.] However, each divine person performs the common work according to his unique personal property. Thus the Church confesses, following the New Testament, "one God and Father from whom all things are, and one Lord Jesus Christ, through whom all things are, and one Holy Spirit in whom all things are". [Council of Constantinople II: DS 421.] It is above all the divine missions of the Son's Incarnation and the gift of the Holy Spirit that show forth the properties of the divine persons.

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266 "Now this is the Catholic faith: We worship one God in the Trinity and the Trinity in unity, without either confusing the persons or dividing the substance; for the person of the Father is one, the Son's is another, the Holy Spirit's another; but the Godhead of the Father, Son and Holy Spirit is one, their glory equal, their majesty coeternal" (Athanasian Creed: DS 75; ND 16).

253 The Trinity is One. We do not confess three Gods, but one God in three persons, the "consubstantial Trinity". [Council of Constantinople II (553): DS 421.] 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." [Council of Toledo XI (675): DS 530:26.] In the words of the Fourth Lateran Council (1215), "Each of the persons is that supreme reality, viz., the divine substance, essence or nature." [Lateran Council IV (1215): DS 804.]

254 The divine persons are really distinct from one another. "God is one but not solitary." [Fides Damasi: DS 71.] "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." [Council of Toledo XI (675): DS 530:25.] 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." [Lateran Council IV (1215): DS 804.] The divine Unity is Triune.

255 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." [Council of Toledo XI (675): DS 528.] Indeed "everything (in them) is one where there is no opposition of relationship." [Council of Florence (1442): DS 1330.] "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." [Council of Florence (1442): DS 1331.]

256 St. Gregory of Nazianzus, also called "the Theologian", entrusts this summary of Trinitarian faith to the catechumens of Constantinople: