Mother of god
Saying that Mary is not the Mother of God(as some protestants do) does not merely diminish a woman, it directly affects the correct understanding of Christ. The issue is not primarily Mary, but Christological.
To deny that Mary is the Mother of God ultimately divides Christ into two: a man and a God, instead of the God-Man, the one divine Person the incarnate Word.
This has profound implications and is not a secondary matter. If there were only a man separated from God, then how could that man save me? If only a man died for me, then salvation would come from a creature and not from God Himself. But no creature can save the world. On the other hand, if God did not truly assume human nature, then He also did not truly suffer and die for us, because God, in His divine nature, neither suffers nor dies. In that case, it would have been merely a man who suffered on the cross.
The Christian faith has always affirmed something different: the One born of Mary is truly God and truly man. These are not two separate persons, but one divine Person, the incarnate Word.
For this reason, the venerable title “Mother of God” is both correct and necessary. Mary is not the mother of the eternal divinity of the Word, but she is the mother of the Person who was born from her, and that Person is God.
If Christ is not God, He cannot save. If He is not man, He cannot die. And if He is not both God and man at the same time, then He can neither die for us nor accomplish our salvation.