Revealed as Trinity
From the Catechism of the Catholic Church, Simplified
Two Meanings of Father (238-239)
Many religions call God "Father" meaning "Creator of the world." God was also "Father" as the giver of the Covenant and of the law to Israel, "his first-born Son." (Ex 4:22) He was "Father to the king" and "Father of the poor."
God as Father means two things. He created everything and has loving care for all. In the Bible, motherhood also expresses God's tenderness. Although God uses the image of human parents, God is neither man nor woman. No one is father as God is Father.
Jesus' Unique Revealing (240-242)
Jesus further revealed God as Father not just as Creator but as eternally Father to Jesus, the only-begotten Son. "No one knows the Son except the Father and no one knows the Father except the Son and anyone to whom the Son chooses to reveal him" (Mt 11:27). Jesus is the "Word" who was "in the beginning with God" and "was God" (Jn 1:1). He is "the image of the invisible God" (Col 1:15).
The Church declared that Jesus was "consubstantial" with the Father (Nicea). Jesus is "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" (Constantinople).
The Revealing of the Spirit (243-245)
Jesus said he would send "another Paraclete" (Jn 14:17, 26; 16-13), and revealed the Spirit as a third person together with the Father and Son. When the Spirit was sent to the Church in person by the Father and the Son (after Jesus' glorification) the mystery of the Trinity was revealed in its fullness.
"We believe in the Holy Spirit, the Lord and giver of life, who proceeds from the Father" (Constantinople).
The Sixth Council of Toledo said that the Father is "the source and origin of the whole divinity." The eternal origin of the Spirit is connected with the Son's origin. "Yet he is not called the Spirit of the Father alone, but the Spirit of both the Father and the Son" (Toledo XI). "With the Father and the Son, he is worshipped and glorified" (Nicene Creed).
Relationship to Father and Son (246)
The Nicene Creed says the "Spirit proceeds from the Father and the Son." The Council of Florence says "the Spirit has his nature and subsistence at the same time (simul) from the Father and the Son. He proceeds eternally from both as from one principle and through one spiration."
Different Formulas (247-248)
The Latin liturgy between 700 and 1200 began to say, "the Holy Spirit who proceeds from the Father and the Son." The earlier Council of Constantinople had used a different formula, "the Holy Spirit proceeded from the Father through the Son." Unfortunately, these different expressions of the same truth have constituted a point of disagreement with the Orthodox Churches.
The Orthodox formula ("through the Son") stresses the Father as the first origin of the Spirit. The Latin formula ("and the Son") stresses the oneness of the Father and the Son. This Latin formula is valid. The Father and the Son are the single principle from which the Spirit proceeds.