Today’s Catechism sections deal with the mystery of God as the Trinity as revealed by Jesus through his incarnation.

II. THE REVELATION OF GOD AS TRINITY

The Father revealed by the Son

238 Many religions invoke God as "Father". The deity is often considered the "father of gods and of men". In Israel, God is called "Father" inasmuch as he is Creator of the world.59 Even more, God is Father because of the covenant and the gift of the law to Israel, "his first-born son".60 God is also called the Father of the king of Israel. Most especially he is "the Father of the poor", of the orphaned and the widowed, who are under his loving protection.61

239 By calling God "Father", the language of faith indicates two main things: that God is the first origin of everything and transcendent authority; and that he is at the same time goodness and loving care for all his children. God's parental tenderness can also be expressed by the image of motherhood,62 which emphasizes God's immanence, the intimacy between Creator and creature. the language of faith thus draws on the human experience of parents, who are in a way the first representatives of God for man. But this experience also tells us that human parents are fallible and can disfigure the face of fatherhood and motherhood. We ought therefore to recall that God transcends the human distinction between the sexes. He is neither man nor woman: he is God. He also transcends human fatherhood and motherhood, although he is their origin and standard:63 no one is father as God is Father.

240 Jesus revealed that God is Father in an unheard-of sense: he is Father not only in being Creator; he is eternally Father by his relationship to his only Son who, reciprocally, is Son only in relation to his Father: "No one knows the Son except the Father, and no one knows the Father except the Son and any one to whom the Son chooses to reveal him."64

241 For this reason the apostles confess Jesus to be the Word: "In the beginning was the Word, and the Word was with God, and the Word was God"; as "the image of the invisible God"; as the "radiance of the glory of God and the very stamp of his nature".65

242 Following this apostolic tradition, the Church confessed at the first ecumenical council at Nicaea (325) that the Son is "consubstantial" with the Father, that is, one only God with him.66 The second ecumenical council, held at Constantinople in 381, kept this expression in its formulation of the Nicene Creed and confessed "the only-begotten Son of God, eternally begotten of the Father, light from light, true God from true God, begotten not made, consubstantial with the Father".67

IN BRIEF

262 The Incarnation of God's Son reveals that God is the eternal Father and that the Son is consubstantial with the Father, which means that, in the Father and with the Father the Son is one and the same God.

St. Gregory Thaumaturgus describes the mystery of the Trinity brought to light by the incarnation of Jesus Christ in his letter “On the Trinity”.

But the person of the Son is composite in its oneness (unita est), being one made up of two, that is, of divinity and humanity together, which two constitute one. Yet the divinity does not consequently receive any increment, but the Trinity remains as it was. Nor does anything new befall the persons even or the names, but these are eternal and without time. No one, however, was sufficient to know these until the Son being made flesh manifested them, saying: Father, I have manifested Your name to men; glorify me also, that they may know me as Your Son. John 17:6 And on the mount the Father spoke, and said, This is my beloved Son. Matthew 3:17 And the same sent His Holy Spirit at the Jordan. And thus it was declared to us that there is an Eternal Trinity in equal honor. Besides, the generation of the Son by the Father is incomprehensible and ineffable; and because it is spiritual, its investigation becomes impracticable: for a spiritual object can neither be understood nor traced by a corporeal object, for that is far removed from human nature.

Footnotes

59 Cf. Dt 32:6; Mal 2:10.
60 Ex 4:22.
61 Cf. 2 Sam 7:14; ⇒ Ps 68:6.
62 Cf. ⇒ Is 66:13; ⇒ Ps 131:2.
63 Cf. ⇒ Ps 27:10; ⇒ Eph 3:14; ⇒ Is 49:15.
64 ⇒ Mt 11-27.
65 ⇒ Jn 1:1; ⇒ Col 1:15; ⇒ Heb 1:3.
66 The English phrases "of one being" and "one in being" translate the Greek word homoousios, which was rendered in Latin by consubstantialis.
67 Niceno-Constantinopolitan Creed; cf. DS 150.