Christianity

> The object of this feast is to commemorate the dignity of the Mary as Mother of God. Mary is truly the Mother of Christ, who in one person unites the human and divine nature. This title was solemnly ratified by the Council of Ephesus, 22 June, 431. The hymns used in the office of the feast also allude to Mary's dignity as the spiritual mother of men. The love of Mary for all mankind was that of a mother, for she shared all the feelings of her son whose love for men led Him to die for our redemption (Hunter, Dogm.Theo. 2, 578).
 
https://www.newadvent.org/cathen/10046a.htm
 
> The feast of the "Maternity of the Blessed Virgin Mary" was established in Portugal in 1914 for celebration on 11 October and was extended to the entire Catholic Church by Pope Pius XI in 1931.
 
> The feast is a celebration of Mary's motherhood of Jesus. The English title "Mother of God" is a translation of the Latin title Dei Genetrix, which means "She Who Generated God", as the corresponding Greek title Θεοτόκος (Theotokos) means "She Who Gave Birth to God". This title was dogmatically adopted at the First Council of Ephesus (431)[4] as a way to assert that Jesus is God, and that his mother can therefore be called Mother of God. The title that the 1 January feast celebrates is thus not only Mariological but also Christological.
 
https://infogalactic.com/info/Solemnity_of_Mary,_Mother_of_God