St. Augustine shows the Virgin Mary was always considered special and exclusively sinless among the Saints even in Christian antiquity, by the Lord's Grace and for His honour, "
We must except the holy Virgin Mary, concerning whom I wish to raise no question when it touches the subject of sins,
out of honour 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) Well, then, if,
with this exception of the Virgin, we could only assemble together all the forementioned holy men and women, and ask them whether they lived without sin while they were in this life, what can we suppose would be their answer? Would it be in the language of our author, or in the words of the Apostle John? I put it to you, whether, on having such a question submitted to them, however excellent might have been their sanctity in this body, they would not have exclaimed with one voice: If we say we have no sin, we deceive ourselves, and the truth is not in us? (1 John 1:

" [De natura et gratia, Migne PL 44:267 See the work Online at New Advent here
http://www.newadvent.org/fathers/1503.htm]
And in one of his last works, interrupted by his passing into eternity, the Great Doctor of Grace - whom the Fifth Ecumenical Council vies in praising along with other Fathers as
"We further declare that we hold fast to the decrees of the four Councils, and in every way follow the holy Fathers, Athanasius ... Cyril, Augustine, Proclus, Leo, and their writings on the true faith." - states "We do not transfer Mary to the devil by the condition of Her birth, for this reason, that that condition is dissolved by the grace of Her new birth" [Against Julian in PL 45:1418 - I can't find this work online, someone can kindly post an online link if they have it]
This is nicely in accord with several other Western Fathers: See for e.g. St. Fulgentius of Ruspe cited here, "By these words [Hail, full of grace], the angel shows that She [Mary] was
altogether excluded from the wrath of the first sentence, and restored to the full grace of blessing." Latin:
"Cum dixit, gratia plena, ostendit ex integro, iram exclusam primę sententię, et plenam benedictionis gratiam restitutam." http://catholicpatristics.blogspot.com/2009/03/immaculate-conception.html Finally, as expected, St. Ambrose of Milan had already preceded his Saintly disciple in teaching a similar doctrine, "a Virgin not only undefiled but
a Virgin whom grace has made inviolate, free of every stain of sin [Latin:
ut incorrupta sit virgo, sed virgo per gratiam ab omni integra labe peccati]." (St. Ambrose, Comm. on Psalm 118, Jurgens, Faith of the Early Fathers, vol 2, page 166)
Here, we see the clear Voice of Tradition, and it is possible to show the East was historically just as strong or at any rate no less strong if not stronger on the Immaculate Conception of the Blessed Virgin Mary, until tragically Russia fell into denial of this Apostolic Truth and then into Communism after His Holiness Saintly Bl. Pope Pius IX dogmatically defined it. Here, we see how necessary also the Papacy and Dogmatic Definitions are. When will Orthodox and other separated Christians happily return to Catholic Unity with Rome by professing the Catholic Faith in the Immaculate Conception of the All-Holy Virgin Mary, called Panagia, Panomomos and Prokathartheisa in the Greek Liturgies. She is even called the Unique All Immaculate in the Byzantine Liturgy on Dec. 9th. Greek Orthodox Priest Fr. Laurent Kleenewick himself documents this nicely in his book, His Broken Body: what do deniers of the Immaculate Conception say?