The Old Testament shows God as one, unique, without equal. “Hear, O Israel! The Lord is our God, the Lord alone” (Dt 6:4; Mk 12:29). He created the world, made a covenant with his people, and is the Father of the poor, the orphan, and the widow.
In the Creeds, we profess our faith in God as “Father almighty.” His fatherhood and power illumine each other by his care for us, by adopting us as sons and daughters in Baptism and by being rich in mercy to forgive our sins. Scripture constantly praises the universal power of God as the “mighty one of Jacob” and the “Lord of hosts” (Gn 49:24; Is 1:24ff.). God’s power is loving, for he is our Father.
God’s parental tenderness can also be expressed by the image of motherhood, 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: no one is father as God is Father. (CCC, no. 239)
Jesus revealed God as Father in a new sense. God is Father in his relation to Jesus, his only begotten Son. At the Last Supper, Jesus calls God “Father” forty-five times (cf. Jn 13-17). The Son is divine, as is the Father (cf. Mt 11:27). In a later chapter, Jesus as the Second Person of the Trinity will be discussed further.
Before the Passion, Jesus promised to send the Holy Spirit as teacher, guide, and consoler. The Spirit’s appearance at Pentecost and at other events in the New Testament gives ample evidence of the Holy Spirit as the third Person of the Trinity…
The mystery of the Holy Trinity is the central mystery of the Christian faith and life. God reveals himself as Father, Son, and Holy Spirit. The doctrine of the Trinity includes three truths of faith.
First, the Trinity is One. We do not speak of three gods but of one God. Each of the Persons is fully God. They are a unity of Persons in one divine nature.
Second, the Divine Persons are distinct from each other. Father, Son, and Spirit are not three appearances or modes of God, but three identifiable persons, each fully God in a way distinct from the others.
Third, the Divine Persons are in relation to each other. The distinction of each is understood only in reference to the others. The Father cannot be the Father without the Son, nor can the Son be the Son without the Father. The Holy Spirit is related to the Father and the Son who both send him forth.
All Christians are baptized in the name of the Father and of the Son and of the Holy Spirit. The Trinity illumines all the other mysteries of faith.
You can read more from the United States Catholic Catechism for Adults, order your own copy, or read questions about it at the United States Conference of Catholic Bishops website.
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