Joining ourselves therefore to the holy Fathers, we all confess alike and with one accord-one and the same Son, our Lord Jesus Christ, perfect in His Godhead,. and, the same, perfect in His Manhood, of reasonable soul and body. Of one nature with His Father in His Godhead, and, the same, of one nature with us in His Manhood, in all things save sin; begotten of the Father before the worlds in His Godhead, and born in these last days, the same, for us men and for our salvation, of Mary the Virgin, Mother of Christ who is God and Man; One and the same Christ, Son, God, Lord Only-begotten; to be acknowledged in two natures without confusion, without change, without mixture, without separation; the distinction of the two natures being by no means done away by the union, but the individuality of either of the two natures being rather preserved, and running together in one Person and two Qnumi; not to be divided or separated into two Sons, but there being one and the same only-begotten Son, our Lord Jesus Christ. (Wigram 297)
It is just and right and proper that Mary should be called "Mother of Christ," for that is the name that shows that there was one Person of unity, who in His human nature was of her nature, and in His Godhead, not of her nature. But seeing that from the first moment of the conception of the Manhood of our Lord, that He took from her, God the Word dwelt in it temple-wise and unitedly, and made it with him one Son eternally, we do say that she was thus "Mother of God" and "Mother of the Manhood." Mother of the Manhood by nature; Mother of God, in that He was united to His manhood from the first moment of its conception; and it is His temple eternally, and He is God and Man unitedly, one Son, one Christ (De unione, VII:22; Wigram 288).