Mary is the true physical mother of Jesus Christ, Who is truly God; hence Mary is the Mother of God. The doctrine was defined at the Council of Ephesus in 431 in order to counter Nestorius, who thought that Mary gave birth to Jesus Christ's human nature only. The Catholic Church responded by stating that persons, and not natures, are conceived and born, and that Jesus Christ was a Divine Person, and God-Man. The purpose of this doctrine was, and is, to safeguard the Divinity of Jesus Christ. As such, it is Christ-centered, not Marycentered. In no way does it imply that Mary is greater than, or prior to, God.