A - Thanks for the question. You are correct that many Protestants follow many of the teachings of Augustine. This is especially trues of many who are reformed Protestant (Calvinist) and Lutherans. They believe that Augustine gives credence to their doctrines and beliefs.
St. Augustine is one of the greatest Catholic Saints and one of the greatest theologians in the history of the Church. Thus, he has been very influential in forming many of the ways we understand Christ, even to this day. Pope Benedict XVI can be considered an Augustinian theologian. Yet, there are many of our Protestant brothers and sisters who seem to claim that Augustine taught the same things that they teach today. This might be accurate for some things, but for many others it is not.
The first, and biggest, of Augustine's teachings that many Protestants like to champion is that of predestination. We must first understand that predestination is accepted by the Catholic Church, but how predestanation works has never been dogmatically decided. In other words, we hold that God predestines humans to salvation, because He knows everything. But, we also hold that humans still have free will. How these two things work themselves out, with all the seeming contradictions, has never been officially declared doctrine by the Church. Therefore, any system that seems to answer the question, is a theological guess and private opinion. Augustine was one of the first to try and answer how predestination might work.
His answer is sometimes called Augustinianism - where he affirms that God actively and and unconditionally elects some people to go to Heaven. This belief is acceptable to the Catholic Church as long as we do not hold that God actively wills some people to hell (sometimes called "double predestination), but that we choose it freely.
Some followers of Calvin and Luther believe that Augustine is a pre-Calvinist. This isn't accurate. While Augustine might have similar ideas, they are not the same. For instance, Augustine would never teach the "perseverance of the saints" that Calvin did - this is sometimes called "once-saved always-saved".
So, while the teachings might be similar, they are not identical.
Also, Augustine also taught:
- Perpetual virginity of Mary
- Catholic Canon of Sacred Scripture
- The Catholic teaching on the Eucharist and Mass
- Baptism is necessary for salvation
- Baptism regenerates us
- Sacred Tradition is an authority as Sacred Scripture is
- Authority of the Pope and Bishops is apostolic
- Praying to Saints and Marian devotion
It is irresponsible to try and claim that Augustine is anything but a Catholic.
I hope this helps.
St. Augustine pray for us!