The Sacrament of Holy Orders:
And they appointed two, Joseph, called Barsabas, who was surnamed Justus, and Matthias. And praying, they said: Thou, Lord, who knowest the hearts of all men, shew whether of these two thou hast chosen, To take the place of this ministry and apostleship, from which Judas hath by transgression fallen, that he might go to his own place. And they gave them lots, and the lot fell upon Matthias, and he was numbered with the eleven apostles.
~The Acts of the Apostles 1: 23-26
As he saith also in another place: Thou art a priest for ever, according to the order of Melchisedech.
I write not these things to confound you; but I admonish you as my dearest children. For if you have ten thousand instructors in Christ, yet not many fathers. For in Christ Jesus, by the gospel, I have begotten you. Wherefore I beseech you, be ye followers of me, as I also am of Christ. For this cause have I sent to you Timothy, who is my dearest son and faithful in the Lord; who will put you in mind of my ways, which are in Christ Jesus; as I teach everywhere in every church.
~1 Corinthians 4: 14-17 (St. Paul refers to himself as a father)
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, 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.