Mothers are the mothers of persons - not simply of natures
All people on Earth are subjects existing as human persons and endowed with human natures.
The Person of the Word Incarnate is, not a human person - like the BVM, or ourselves - but, a Divine Person, God the Eternal Word of the Father:
The BVM is therefore the human, created, mother in time & space, of the Divine, Uncreated, Eternal, Incomparable Word through Whom all creation came to be.
She can therefore aptly and accurately be called “God-bearer” AKA Theotokos AKA Deipara AKA Dei genitrix - or in plain English, “mother of God”.
This is no more startling or blasphemous than saying that God’s Word in Scripture comes to us through the words of men. If is acceptable to say that God’s Word written comes to men through God-breathed words that are composed and written by men, why does it trouble some Christians to hear that God’s Eternal Divine Word comes to men through the body and blood and obedience of another human being; the Blessed Virgin Mary ?
In both cases, Something Divine comes from God, by the power and grace of the Spirit of God, working in and through human beings, into the world God has created.
If Isaiah or Paul does not have to be God when God’s Word comes into the world through his human agency and personality - why does the BVM have to be God when the Divine Word is born into the world through her human agency and personality ?
In neither case is the inspired author or the BVM the Primary Author of Scripture or of the Incarnation. God alone is the Primary Author of both Scripture & the Incarnation. The human authors of the Scriptures, and the BVM, are secondary, instrumental causes: in their cases, of the Scriptures, and, in her case, of the Incarnation.
Through the Incarnation, there is no change in God - what is changed, is creation. God was not altered by creation - creation was altered, by being created. Neither does the Incarnation change God - but instead, God creates a new manner of being present to His creation. Creation is changed by this Divine ingenuity - but God is not. The Eucharistic Presence, and its multiplication by the consecration of many Hosts, is an extension of the Incarnation, as is the Church.
An author who puts himself into his own story is not lessened or multiplied or changed thereby - his story is changed. That is a faint picture of how God is not changed by putting Himself, as a man, into the story He has invented.
