2 “Lord, You have tried me, and known me”. Let the Lord Jesus Christ Himself say this; let Him too say, “Lord,” to the Father. For His Father is not His Lord, save because He has deigned to be born according to the flesh. He is Father of the God, Lord of the Man. Would you know to whom He is Father? To the coequal Son. The Apostle says, “Who, being in the form of God, thought it not robbery to be equal with God.” To this “Form” God is Father, the “Form” equal to Himself, the only-begotten Son, begotten of His Substance. But forasmuch as for our sakes, that we might be re-made, and made partakers of His Divine Nature, being renewed unto life eternal, He was made partaker of our mortal nature, what says the Apostle of Him? He says, “yet He emptied Himself, and took upon Him the form of a servant, and was made in the likeness of men, and was found in fashion as a man.” He was in the Form of God, equal to the Father; He took upon Him the form of a servant, so as therein to be less than the Father....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)