Stretching out His hand over His disciples, the Lord Christ declared: “Here are my mother and my brothers. For whoever does the will of my Father in Heaven is my brother and sister and mother” (Mt 12:49-50). I would urge you to ponder these words. Did the Virgin Mary, who believed by faith and conceived by faith, who was the chosen one from whom our Savior was born among men, who was created by Christ before Christ was created in her—did she not do the will of the Father? Indeed the Blessed Virgin certainly did the Father's will, and so it was for her a greater thing to have been Christ's disciple than to have been his mother, and she was more blessed in her discipleship than in her motherhood. …
Mary heard God's word and kept it, and so she is blessed. She kept God's truth in her mind, a nobler thing than carrying His body in her womb. The truth and the body were both Christ: He was kept in Mary's mind insofar as He is truth, He was carried in her womb insofar as He is man…
Mary is both holy and blessed, and yet the Church is greater than she. She is a part of the Church, a member of the Church, a holy, an eminent—the most eminent—member, but still only a member of the entire body. The body undoubtedly is greater than she, one of its members. This body has the Lord for its head, and head and body together make up the whole Christ. In other words, our head is divine—our head is God.
Now, dear brethren, give me your whole attention, for you also are members of Christ; you also are the body of Christ. You, to whom I am speaking, are the members of Christ. Of whom were you born? "Of Mother Church," I hear the reply of your hearts. You became sons of this mother at your baptism, you came to birth then as members of Christ…
This holy, honored Mother, like Mary, gives birth and still is a virgin... Keep virginity in your hearts; the virginity of the spirit is the integrity of the Catholic faith.
Saint Augustine, bishop (Sermo 25,7-8: PL 46, 937-938: She who believed by faith, conceived by faith - excerpt)