The term “Mother of God” is a translation of Mater Dei. But the Greek term is Theotokos, which is more literally translated as “God-bearer.” The term means that she gave birth to the God-man Jesus. Some would say, well she was the mother of Jesus but not God. No one says that she was the Mother of the Holy Trinity, only the mother of Jesus. But we also teach the Jesus was true God, and true man. Man in the round, body and soul. So Mary is central to the Incarnation. The ark of the New Covenant.
See post #183 above.