9 But what matters of deep moment are contained in the Lord's prayer! How many and! How great, briefly collected in the words, but spiritually abundant in virtue! so that there is absolutely nothing passed over that is not comprehended in these our prayers and petitions, as in a compendium of heavenly doctrine. “After this manner,” says He, “pray: Our Father, which art in heaven.” The new man, born again and restored to his God by His grace, says “Father,” in the first place because he has now begun to be a son.
“He came,” He says, “to His own, and His own received Him not. But as many as received Him, to them gave He power to become the sons of God, even to them that believe in His name.” The man, therefore, who has believed in His name, and has become God's son, ought from this point to begin both to give thanks and to profess himself God's son, by declaring that God is his Father in heaven; and also to bear witness, among the very first words of his new birth, that he has renounced an earthly and carnal father, and that he has begun to know as well as to have as a father Him only who is in heaven, as it is written: They who say unto their father and their mother, I have not known you, and who have not acknowledged their own children these have observed Your precepts and have kept Your covenant.
Also the Lord in His Gospel has bidden us to call “no man our father upon earth, because there is to us one Father, who is in heaven.” And to the disciple who had made mention of his dead father, He replied, “Let the dead bury their dead;” for he had said that his father was dead, while the Father of believers is living.
Source: The Treatises of Cyprian (New Advent)