CCC 2780 We can invoke God as “Father” because he is revealed to us by his Son become man and because his Spirit makes him known to us. The personal relation of the Son to the Father is something that man cannot conceive of nor the angelic powers even dimly see: and yet, the Spirit of the Son grants a participation in that very relation to us who believe that Jesus is the Christ and that we are born of God.1

CCC 2781 When we pray to the Father, we are in communion with him and with his Son, Jesus Christ.2 Then we know and recognize him with an ever new sense of wonder. The first phrase of the Our Father is a blessing of adoration before it is a supplication. For it is the glory of God that we should recognize him as “Father,” the true God. We give him thanks for having revealed his name to us, for the gift of believing in it, and for the indwelling of his Presence in us.

CCC 2782 We can adore the Father because he has caused us to be reborn to his life by adopting us as his children in his only Son: by Baptism, he incorporates us into the Body of his Christ; through the anointing of his Spirit who flows from the head to the members, he makes us other “Christs.”
God, indeed, who has predestined us to adoption as his sons, has conformed us to the glorious Body of Christ. So then you who have become sharers in Christ are appropriately called “Christs.”3
The new man, reborn and restored to his God by grace, says first of all, “Father!” because he has now begun to be a son.4

1 Cf. Jn 1:1; 1 Jn 5:1.
2 Cf. 1 Jn 1:3.
3 St. Cyril of Jerusalem, Catech. myst. 3, 1: PG 33, 1088A.
4 St. Cyprian, De Dom. orat. 9: PL 4, 525A.