The Enchiridion by St. Augustine
Chapter 35.--Jesus Christ, Being the Only Son of God, is at the Same Time Man.
Wherefore Christ Jesus, the Son of God, is both God and man; God before all worlds; man in our world: God, because the Word of God (for |the Word was God| ); and man, because in His one person the Word was joined with a body and a rational soul. Wherefore, so far as He is God, He and the Father are one; so far as He is man, the Father is greater than He. For when He was the only Son of God, not by grace, but by nature, that He might be also full of grace, He became the Son of man; and He Himself unites both natures in His own identity, and both natures constitute one Christ; because, |being in the form of God, He thought it not robbery to be,| what He was by nature, |equal with God.| But He made Himself of no reputation, and took upon Himself the form of a servant, not losing or lessening the form of God. And, accordingly, He was both made less and remained equal, being both in one, as has been said: but He was one of these as Word, and the other as man. As Word, He is equal with the Father; as man, less than the Father. One Son of God, and at the same time Son of man; one Son of man, and at the same time Son of God; not two Sons of God, God and man, but one Son of God: God without beginning; man with a beginning, our Lord Jesus Christ.