Nestorianism

Another early heresy was Nestorianism, named (again) after its founder, Nestorius. This doctrine maintained that Jesus had two hypostases (persons) - a divine one and a human one. Nestorius hated the word Theotokos, which is Greek for mother of God. From Nestorius's view, if Jesus had two separate natures, then the most Mary could do was give birth to the human person of Jesus, and not the divine.

Another ecumenical council was convened in 431 A.D., this time in Ephesus, and the participants hammered out a doctrine that dictated Jesus had only one person, not two, and consisted of two natures-human and divine. Since Christ was only one person, Mary could still be said to be the Mother of God, because she gave birth to that one person. In other words, Jesus didn't come in two parts, but in one body with two distinct natures. The Church calls Mary the Mother of God, since she gave birth to the human Jesus, but she was not the source of his divinity. This is not a contradiction: consider how your own mother gave birth to you, but God gave you a soul.