The Council of Ephesus is sometimes remembered simply as a council "about Mary."
That misses the center of the controversy.
It was fundamentally about Jesus Christ.
Who Is the One Mary Bore?
The title Theotokos --- God-bearer or Mother of God --- protected the confession that the one born of Mary is the divine Son incarnate.
Mary did not create God.
She is not divine.
The question was whether Jesus Christ is one Person who is truly God and truly man.
Why This Matters to the Timeline
By AD 431 Christianity is already using:
- ecumenical councils;
- bishops;
- inherited creeds;
- earlier Fathers;
- theological terminology;
- appeals to received faith;
to settle profound Christological disputes.
A Division Also Follows
The controversies surrounding Ephesus contributed to enduring divisions among ancient Christian communities.
This is important: Christian division did not begin with Luther.
Vatican II explicitly recognizes early Eastern divisions associated with the doctrinal formulas of Ephesus and Chalcedon.