When did Augustine write this?
Augustine was a prolific writer and he has made numerous comments which relate directly to the issue of the interpretation of the rock of Matthew 16:18. In fact, Augustine made more comments upon this passage than any other Church father.
At the end of his life, Augustine wrote his Retractations where he corrects statements in his earlier writings which he says were erroneous. One of these had to do with the interpretation of the rock in Matthew 16. At the beginning of his ministry Augustine had written that the rock was Peter. However, very early on he later changed his position and throughout the remainder of his ministry he adopted the view that the rock was not Peter but Christ or Peter’s confession which pointed to the person of Christ. The following are statements from his Retractations which refer to his interpretation of the rock of Matthew 16:
In a passage in this book, I said about the Apostle Peter: ‘On him as on a rock the Church was built’...But I know that very frequently at a later time, I so explained what the Lord said: ‘Thou art Peter, and upon this rock I will build my Church,’ that it be understood as built upon Him whom Peter confessed saying: ‘Thou art the Christ, the Son of the living God,’ and so Peter, called after this rock, represented the person of the Church which is built upon this rock, and has received ‘the keys of the kingdom of heaven.’ For, ‘Thou art Peter’ and not ‘Thou art the rock’ was said to him. But ‘the rock was Christ,’ in confessing whom, as also the whole Church confesses, Simon was called Peter. But let the reader decide which of these two opinions is the more probable (The Fathers of the Church (Washington D.C., Catholic University, 1968), Saint Augustine, The Retractations Chapter 20.1).
Clearly Augustine is repudiating a previously held position, adopting the view that the rock was Christ and not Peter.
You might have been quoting an EARLIER piece that he wrote, not the RETRACTIONS he wrote at the end of his life.
Also, notice that Augustine gave the reader the FREEDOM to determine which understanding he believes is correct, he never imposed his own personal understanding on others.
“”At the end of his life, Augustine wrote his Retractations where he corrects statements in his earlier writings which he says were erroneous.””
Dear,seek,Blessed Augustine Retractationes did not denounce any Catholic teaching Augustine held,they were only Blessed Augustine’s effort to explain the work in some of his previous writings. Augustine never wrote anything denouncing the primacy of Saint Peter and the succession of the primacy.
Here is Augustine’s 53 letter again- Blessed Augustine never retraced any of this at all!
St Augustine Letter 53..
http://ww.newadvent.org/fathers/1102053.htm
For if the lineal succession of bishops is to be taken into account, with how much more certainty and benefit to the Church do we reckon back till we reach Peter himself, to whom, as bearing in a figure the whole Church, the Lord said: “Upon this rock will I build my Church, and the gates of hell shall not prevail against it!” Matthew 16:18 The successor of Peter was Linus, and his successors in unbroken continuity were these:— Clement, Anacletus, Evaristus, Alexander, Sixtus, Telesphorus, Iginus, Anicetus, Pius, Soter, Eleutherius, Victor, Zephirinus, Calixtus, Urbanus, Pontianus, Antherus, Fabianus, Cornelius, Lucius, Stephanus, Xystus, Dionysius, Felix, Eutychianus, Gaius, Marcellinus, Marcellus, Eusebius, Miltiades, Sylvester, Marcus, Julius, Liberius, Damasus, and Siricius, whose successor is the present Bishop Anastasius. In this order of succession no Donatist bishop is found. But, reversing the natural course of things, the Donatists sent to Rome from Africa an ordained bishop, who, putting himself at the head of a few Africans in the great metropolis, gave some notoriety to the name of “mountain men,” or Cutzupits, by which they were known.
The biggest issue with Blessed Augustine was his lack of understanding in Greek-this is where he sometimes runs into trouble with some of his writings and where our fellow Eastern Orthodox rightfully take issue as well.
I suggest you go back and read Augustine sermon 26 since I think this is where Augustine lack of Greek understanding seems to be shown a little
Augustine Sermon 26
http://www.newadvent.org/fathers/160326.htm
He still comes to the conclusion in 26 to uphold Saint Peter as chiefest Apostle, which also coincides with his letter 53
“In that one Apostle then, that is, Peter, in the order of Apostles first and chiefest, in whom the Church was figured, both sorts were to be represented, that is, both the strong and weak; because the Church does not exist without them both.” Saint Augustine letter 26