Theotokos is one of the oldest titles given to Mary, going back to the third century. It’s often roughly translated into English as “Mother of God,” but a more accurate translation means “God-bearer.” The solemnity of Mary, Mother of God is celebrated on January 1, which is also the day of Jesus’ circumcision.
I think both translations of Theotokos reflect interesting aspects of Mary and Christ. One question I often had as a kid (and I think a lot of Christian kids do) was “Who was God’s mommy?” which was really a way of asking, “Where did God come from?” or “What came before God?” The concept of an eternal being is hard to impress upon kids who haven’t developed abstract thinking yet. But interesting, although God has no beginning, he does have a mother. Jesus is fully God, therefore, the mother of Jesus is the mother of God. She was the one who carried God Incarnate in her womb, who raised him as a child, who urged him to perform his first miracle, who followed him to the cross.
“God-bearer” focuses again on the incarnation part of her role as Christ’s mother. She literally bore God into his own creation. She served as the Ark of the New Covenant. God used Mary to unite the Word and flesh. The term Theotokos was affirmed at the Council of Ephesus in in 431. The council primarily dealt with Christ’s nature as fully God and fully man. Affirming Mary as the Theotokos was a logical conclusion of the affirmation of the Nicene Creed and hypostatic union.