Anyone with a bit of good sense would not make so bold as to call God by the name of Father until he had come to be like him.
It is impossible for God who is goodness in his very being to be father to someone of evil will. It is impossible for the Holy One to be father of a depraved person. It is impossible for the Giver of life to have as a child one whose sin has subjected him to death.
So if one of us, in examining himself, discovers that his conscience is covered in mud and needs to be cleansed, he cannot allow himself such familiarity with God. First he must be purified.
Then why, in this prayer of his, does the Lord Jesus teach us to call God by the name of Father? I suppose that, in suggesting this word, he is only putting before our eyes the holiest life as the criterion of our behavior.
[Breviario Patristico © 1971 Piero Gribaudi
Editore, Turin, Italy; translated by Paul Drake]