One day the apostles asked Jesus how they should pray. Christ then taught them the Our Father. This prayer first lifts our heart to honor God and his will and then we presents to him our needs of both body and soul. In what follows, I will try to give a partial insight into each phrase of this most perfect prayer.
Is the name Father, the proper name of the divine person?
The name Father defines divine relationships; since God the Father begot the Son from all eternity and with the Son spirates the Spirit, his proper name is Father. (see Summa Theologica, Q.33.Art. 2)
Christ said, "No one knows the Son except the Father, and no one knows the Father except the Son." The knowledge that Christ has of his Father is a living communion of infinite life, power, love, joy and peace beyond our limited understanding. When Christ speaks of God his Father he is telling us that He is the only begotten Son from all eternity. To call God mother would not have the same meaning. Further, Christ has one Father and a human mother (Mary) and to call God Mother would distort this divine dynamics between man and God.
We invoke the "Father" in a familiar and affectionate way because the Spirit makes it possible for us to do so. With, in and through Christ we have become adopted sons/daughters of the Father and so with confidence we call him Father.
Who Art In Heaven