St. Augustine (354-430) is considered to be the greatest of the Western Fathers. He had a considerable influence on the development of Catholic theology and on spiritual doctrine. He did not write a treatise on the Virgin Mary, but he left several profound pages on the Mother of the Incarnate Word.
On Mary’s immaculate conception:
We must except the holy Virgin Mary, concerning whom I wish to raise no question when it touches the subject of sins, out of honor to the Lord; for from Him we know what abundance of grace for overcoming sin in every particular was conferred upon her who had the merit to conceive and bear Him who undoubtedly had no sin. 1 John 3:5 (On Nature and Grace, 42)
On the fruitful virginity of the Church and of Mary:
2. Whereas, therefore, the whole Church itself is a virgin espoused unto one Husband Christ, as the Apostle says, of how great honor are its members worthy, who guard this even in the flesh itself, which the whole Church guards in the faith? Which imitates the mother of her husband, and her Lord.
For the Church also is both a mother and a virgin. For whose virgin purity consult we for, if she is not a virgin? Or whose children address we, if she is not a mother? Mary bare the Head of This Body after the flesh, the Church bears the members of that Body after the Spirit.
In both virginity hinders not fruitfulness: in both fruitfulness takes not away virginity. Wherefore, whereas the whole Church is holy both in body and spirit, and yet the whole is not virgin in body but in spirit; how much more holy is it in these members, wherein it is virgin both in body and spirit?
3. It is written in the Gospel, of the mother and brethren of Christ, that is, His kindred after the flesh, that, when word had been brought to Him, and they were standing without, because they could not come to Him by reason of the crowd, He made answer: “Who is My mother? Or who are My brethren? And stretching forth His Hand over His disciples, He says: These are My brethren: and whosoever shall have done the will of My Father, that man is to Me brother, and mother, and sister.” (Mt 12: 48-50)
What else teaching us, than to prefer to kindred after the flesh, our descent after the Spirit: and that men are not blessed for this reason, that they are united by nearness of flesh unto just and holy men, but that, by obeying and following, they cleave unto their doctrine and conduct. Therefore Mary is more blessed in receiving the faith of Christ, than in conceiving the flesh of Christ.
For to a certain one who said: “Blessed is the womb, which bare You,” He Himself made answer, “Yea, rather, blessed are they who hear the Word of God, and keep it.” (Lk 11:27-28) Lastly, to His brethren, that is, His kindred after the flesh, who believed not in Him, what profit was there in that being of kin?
Thus also her nearness as a Mother would have been of no profit to Mary, had she not borne Christ in her heart after a more blessed manner than in her flesh.
(Of Holy Virginity, 2-3)