Complex sentence: He was condemned by Cyril of Alexandria and the Council of Ephesus (431) for refusing to call the Virgin Mary by the title "mother of God"; he would only call her "mother of Christ".
Split into simpler sentences: He was condemned by Cyril of Alexandria and the Council of Ephesus (431) for refusing to call the Virgin Mary, by the title "mother of God". He would only call her "mother of Christ".