CCC 240
© Libreria Editrice Vaticana Source: vatican.va
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." Mt 11-27.
Read the full chapter 1. I Believe in God the Father ¶198–421