Ambrose on the incarnation

Letter of Ambrose to Sabinus, a Bishop. ca. AD 390

Just as in the form of God, He lacked nothing of the divine nature and its fullness, so too in the form of man there was nothing lacking in Him, by the absence of which He might have been judged an imperfect man; for He came to save the whole man. It would not have been fitting for One who accomplished a perfect work in others to allow anything imperfect in Himself. If something was lacking in His humanity, He did not redeem the whole man; and if He did not redeem the whole man, He was a deceiver when He declared that He had come to save the whole man. But He did not deceive, because “It is not possible for God to lie. ” Because He came, therefore, to save and redeem the whole man, it follows that He took upon Himself the whole man, and that His humanity was perfect.—Ambrose in William A. Jurgens, Faith of the Early Fathers, 2:148