One God in Three Persons: the Father, the Son and the Holy Spirit.
Jesus Christ is true God and true man.
The central mystery of Christian faith and life is the mystery of the Most Blessed Trinity. Christians are baptized in the name of the Father and of the Son and of the Holy Spirit.
God has left some traces of his trinitarian being in creation and in the Old Testament but his inmost being as the Holy Trinity is a mystery which is inaccessible to reason alone or even to Israel's faith before the Incarnation of the Son of God and the sending of the Holy Spirit. This mystery was revealed by Jesus Christ and it is the source of all the other mysteries.
Jesus Christ revealed to us that God is “Father”, not only insofar as he created the universe and the mankind, but above all because he eternally generated in his bosom the Son who is his Word, “ the radiance of the glory of God and the very stamp of his nature” (Hebrews 1:3).
The Holy Spirit is the third Person of the Most Blessed Trinity. He is God, one and equal with the Father and the Son. He “proceeds from the Father” (John 15:26) who is the principle without a principle and the origin of all trinitarian life. He proceeds also from the Son (Filioque) by the eternal Gift which the Father makes of him to the Son. Sent by the Father and the Incarnate Son, the Holy Spirit guides the Church “to know all truth” (John 16:13).
The Church expresses her trinitarian faith by professing a belief in the oneness of God in whom there are three Persons: Father, Son, and Holy Spirit. The three divine Persons are only one God because each of them equally possesses the fullness of the one and indivisible divine nature. They are really distinct from each other by reason of the relations which place them in correspondence to each other. The Father generates the Son; the Son is generated by the Father; the Holy Spirit proceeds from the Father and the Son.
Inseparable in their one substance, the three divine Persons are also inseparable in their activity. The Trinity has one operation, sole and the same. In this one divine action, however, each Person is present according to the mode which is proper to him in the Trinity.
The baptism is given in the name of the Father and the Son and the Holy Spirit (Mt 28, 19).
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The Old Testament already contains some signs of the mystery of the Holy Trinity, for example by the surprising juxtaposition of words in the singular and plural in the book of Genesis:
- The Creator is designated by a plural word "Elohim", but He acts in the singular:"He created" (bara) (1,1).
- At the time of the creation of man, God said: "Let us make man in our image, after our likeness" (1,26).
- After the fall of Adam and Eve, God said: "Behold, the man has become like one of us" (3,22 a).
- At the time of the tower of Babel, God said: "Let us go, descend and confuse their language, so that they do not hear any more the language of the ones and others" (11.7 a).
- Later, three men appear to Abraham by the oaks of Mamre, (Gen 18,2-14). And yet Abraham speaks to them in the singular: "My Lord", as if they did only one. Abraham sees three men, but only one adores any. But them, they speak with one voice: “They asked him”. They announce the birth of Isaac to Abraham and Sara, while she is too old to have a child. This miraculous birth precedes the birth of Jesus, because "it does not have there nothing too marvellous for God".
The first revelation of the Trinity is made at the Annunciation to Mary by the voice of the angel Gabriel:
"The Holy Spirit will come upon you, and the power of the Most High will overshadow you; therefore the child to be born will be called holy, the Son of God" (Luke 1, 35).
We are in the presence of the Father in Heaven, the Son in the womb of Mary and the Holy Spirit descending from heaven to Mary.
The revelation of the Trinity is also at the baptism of Jesus: the Holy Spirit descended upon him in bodily form, as a dove, and a voice came from heaven,
"Thou art my beloved Son; with thee I am well pleased" (Luke 3,22).
The divinity of the Son is confirmed at the Transfiguration: a voice came out of the cloud, saying, "This is my Son, my Chosen; listen to him!" (Luke 9,35).
