5 The Only-begotten God, therefore, when He was born man of the Virgin, and in the fullness of time was about in His own person to raise humanity to divinity, always maintained this form of the Gospel teaching. He taught, namely, to believe Him the Son of God, and exhorted to preach Him the Son of Man; man saying and doing all that belongs to God; God saying and doing all that belongs to man. Yet never did He speak without signifying by the twofold aspect of these very utterances both His manhood and His divinity. Though He proclaimed one God the Father, He declared Himself to be in the nature of the one God, by the truth of His generation. Yet in His office as Son and His condition as man, He subjected Himself to God the Father, since everything that is born must refer itself back to its author, and all flesh must confess itself weak before God. Here, accordingly, the heretics find opportunity to deceive the simple and ignorant. These words, uttered in His human character, they falsely refer to the weakness of His divine nature; and because He was one and the same Person in all His utterances, they claim that He spoke always of His entire self.
Source: On the Trinity (New Advent)