The Holy Catholic Church has been consistently attacked by the ignorant anti-Catholics because of her teaching that the Blessed Virgin Mary is the mother of God; for according to them, calling Mary with that title is also treating her as goddess which is of course no different from what pagans do. The opponents of the doctrine also argued that God is the ultimate source of all things; thus, He Himself has no beginning and consequently has no mother. But why is Mary called the mother of God?
The Blessed Virgin Mary is the mother of God precisely because Jesus Christ, her Son, is God. When Mary gave birth to Him, she did not give birth to a nature, or even to two natures; but she gave birth to one Divine Person.
In Luke 1:43, Elizabeth “exclaimed [to Mary] with a loud cry, ‘Blessed are you among women, and blessed is the fruit of your womb! And why is this granted me, that the mother of my Lord should come to me?’” Note that in the New Testament, the term “lord” (Greek, kýrios) was used in the context of divinity at times, but it is also used with reference to human persons in various contexts. Yet, when the term is used in reference to the divinity, it would appear so obvious. For instance, in 1 Corinthians 8:5, it reads: “For although there may be so-called gods in heaven or on earth—as indeed there are many ‘gods’ and many ‘lords’ . . .” Here the term “lord” (kýrios) is obviously not used to refer to divinity. But the next words in the same verse state: “Yet to us there is one God, the Father, from whom are all things, and for whom we exist, and one Lord, Jesus Christ, through whom are all things and through whom we exist.” Note that Jesus is called both the one Lord [(ένας Κύριος) (énas Kýrios)] and creator of all things. Thus, there can be no doubt that the term “Lord” refers to Christ’s divinity. The same term can also be certainly found in Deuteronomy 4:6 — “Hear, O Israel: The Lord our God is one Lord” [(Άκου, Ισραήλ: Ο Κύριος ο Θεός μας είναι ένας Κύριος) (Ákou, Israíl: O Kýrios o Theós mas eínai énas Kýrios)]. Hence, Mary being the mother of the Lord is indeed the mother of God. In Greek, from which the Gospel was originally written, it is translated as “Η μητέρα του Κυρίου” (I mitéra tou Kyríou).
However, Mary’s motherhood of God does not immediately mean motherhood of the Most Holy Trinity because she is only the mother of the second Person of the Blessed Trinity; for neither the Father nor the Holy Spirit has come into flesh. It does not also imply that she came before God or the source of her Son’s divinity because she doesn’t have to be in order to be the mother of the second Person of God made flesh. Though she did not provide Christ with either His divine nature or His immortal human soul, she is still His mother because she did not give birth to a mere human body, a soul, a nature, or even two natures but gave birth to a Person and that one Person is God.
Thus, denying Mary as the mother of God and affirming her to be only the mother of the human nature of Jesus Christ is absolutely denying the divinity of Him Who was crucified for humanity’s sake. Indeed, Christ is one divine person with two nature — one human, and one divine — hypostatically unified, or joined together without admixture in His one divine Person. Colossians 2:9 states: “For in Christ lives all the fullness of God in a human body.”
As summed up in the Catechism of the Catholic Church:
“Called in the Gospels “the mother of Jesus,” Mary is acclaimed by Elizabeth, at the prompting of the Spirit and even before the birth of her son, as “the mother of my Lord.” In fact, the One whom she conceived as man by the Holy Spirit, who truly became her Son according to the flesh, was none other than the Father’s eternal Son, the second Person of the Holy Trinity. Hence the Church confesses that Mary is truly “Mother of God” (Theotokos)” (CCC 495).