For the Savior said, “When you pray, say, ‘Our Father.’ ” And another of the holy Evangelists adds, “who art in heaven.”…

He gives his own glory to us. He raises slaves to the dignity of freedom. He crowns the human condition with such honor as surpasses the power of nature. He brings to pass what was spoken of old by the voice of the psalmist: “I said, you are gods, and all of you children of the Most High.” (Psalm 82:6) He rescues us from the measure of slavery, giving us by his grace what we did not possess by nature, and permits us to call God “Father,” as being admitted to the rank of sons. We received this, together with all our other privileges, from him. One of these privileges is the dignity of freedom, a gift peculiarly befitting those who have been called to be sons.

He commands us, therefore, to take boldness and say in our prayers, “Our Father.” We, who are children of earth and slaves and subject by the law of nature to him who created us, call him who is in heaven “Father.” Most fittingly, he enables those who pray to understand this also. Since we call God “Father” and have been counted worthy of such a distinguished honor, we must lead holy and thoroughly blameless lives. We must behave as is pleasing to our Father and not think or say anything unworthy or unfit for the freedom that has been bestowed on us….

The Savior of all very wisely grants us to call God “Father,” that we, knowing well that we are sons of God, may behave in a manner worthy of him who has honored us. He will then receive the supplications that we offer in Christ.

[COMMENTARY ON LUKE, HOMILY 71]