Describing the Church as a mother seems to come from the Bible, such as Galatians 4:26, 31 and Revelation 12:1-17, especially verse 17.
In the treatise On Re-Baptism by an anonymous writer, written about A.D. 255, these phrases appear: “our most holy mother the Church,” “our mother the Church” (paragraph 1), and “our most holy mother Church” (paragraph 6).
St. Cyril of Jerusalem, writing about A.D. 347, in his Catechetical Lecture 18, describes the Holy Catholic Church as “the mother of us all,” seemingly because, when we were baptized in the Catholic Church, we “were regenerated,” that is, born again (paragraph 26).
DISCLAIMER: Catholic Answers has turned over the archive to Catholic-Questions.org and no longer owns, manages, or moderates the forums. For additional apologetics resources please visit www.catholic.com.