Mary, the Holy Mother of God

The Blessed Virgin Mary is honored as the Mother of God because she conceived and gave birth to Christ, who is the incarnation of God the Son, the Second Person of the Blessed Trinity.  It is fitting to honor Mary as Mother of Jesus, following the birth of Christ.  When Catholics celebrate the Solemnity of Mary Mother of God, we are not only honoring Mary, who was chosen among all women throughout history to bear God incarnate, but we are also honoring our Lord, who is fully God and fully human.

Since the first centuries of Christianity, the Church customarily has regarded the Blessed Virgin Mary to be the Mother of God for a simple, logical reason;
By the power of the Holy Spirit, she conceived Jesus Christ, the Son of God.

Since the divine Person, God the Son, assumed, or took on, human nature, she is the Mother of God in the fullest since: "What the Catholic faith believes about Mary is based on what it believes about Christ, and what it teaches about Mary illumines in turn its faith in Christ" (CCC 487). The Church solemnly defined this belief at the Ecumenical Council of Ephesus AD 431.