It is no coincidence that the preceding books philosophically correspond to the Seven Ages of Man - infancy, childhood, lover (adolescence), soldier (young adult), justice (adult), old age, and dementia/death. Augustine's Books parallel the philosophical nature of these states rather than the physical. Book VIII begins with an impassioned praise of thanks to God for allowing him to be converted. Biblical quotes come thick and fast, and it is clear that we are to be told how, at long last, Augustine has come to God.
At no point during the previous seven books does Augustine ever say that he does not believe in God. In fact, during this long process of conversion the change in Augustine has been one of degree rather than kind. He has always believed in a Supreme Deity, but the nature of that Deity and how he should worship it has been a challenging matter. We are told that even during his Manichaean Hearer days he was unsure of the true nature of God, and never wholly surrendered himself to that religion. He has been seeking a faith that answers all of his questions, and he has, even in his sinful moments, been open to the idea of finding the truth in God.
In this Book Augustine has finally removed all doubts that God does indeed have "spiritual substance" - meaning that He does exist in an immaterial way. That this substance is the beginning of all things now seems evident to him. The idea that God isn't limited by the spatial relationships that everything on Earth is limited by is finally resolved in Augustine's mind. Now that he has resolved some of his philosophical issues about God, he hopes that he can be firmer in his practice of morality.
Augustine visited an aged and highly venerated priest of Milan named Simplicianus who had baptized the Bishop Ambrose. Augustine tells Simplicianus of his theological agonies, and Simplicianus replies by telling Augustine the story of Victorinus, a famous and erudite translator of Neoplatonic books. Augustine had been reading some of these books recently. In his seventies, Victorinus converted to the Catholic faith. Augustine was deeply affected by this story because Victorinus was as educated and intellectual a man as ever became a Christian. The fact that a man of such philosophical and intellectual prowess would come to the faith emboldened Augustine to do the same. Augustine says he was "ardent to follow [Victorinus'] example."
At this time Augustine's friends Nebridius and Alypius were also trying to establish a contemplative life. Augustine not only had an internal desire to convert, but also enjoyed the external assistance of Simplicianus and his close companions. Everyone around him appeared to be leading him towards God. However, Augustine did not convert just yet. He received a visit from a high official and fellow African, Ponticanius, who told him that certain officials in the Emperor's court had been reading the Scripture and had been "set on fire," instantly embracing the faith and the monastic life. Augustine reacted negatively, although he expressed affection for these young men. He was ashamed to look at himself and admit his lack of dedication to God.
Augustine looks back on his prayers to God up until now and writes what is perhaps his most famous line: "Grant me chastity and continence, but not yet." After his visit from Ponticanius he seemed aware that he was going to convert, but it as if he could not yet bring himself to admit it. He felt as if he had two identities battling within himself; one that yearned for conversion, and the other that desired secular ambition and pleasures. However, he acknowledged that to recognize two wills is to fall into the duality of good and evil that the Manichees espouse (in error, according to Augustine).
Augustine conversed with Alypius and became so agitated that he was physically ill. He still had some vestiges of intellectual snobbery. He cried out to Alypius, "What is wrong with us?...Uneducated people are rising up and capturing heaven and we with our high culture without any heart - see where we roll in the mud of flesh and blood. Is it because they are ahead of us that we are ashamed to follow?" Augustine decided to walk in the garden to calm down, but was so agitated that he tore at his clothes and hair and beat himself. He tried to quiet his earthly desires, and rhetorically referred to Lady Continence coming to embrace him and telling him to "Make the leap without anxiety."
Augustine was overcome, and went to a bench to weep. From a neighboring house (or a church, or the very heavens themselves) he heard a child saying "Pick up and read" (a statement foreshadowed earlier in the book). This he interpreted as a divine command, and he picked up the Book of Paul. Augustine opened the book just as many Christians do today with their Bibles and read the first passage that his eye fell upon. "Not in riots and drunken parties, not in eroticism and indecencies, not in strife and rivalry, but put on the Lord Jesus Christ and make no provision for the flesh in its lusts" (Rom 13 13-14).
With this, all of Augustine's doubts were expelled, and he was converted. He told Alypius the good news, and Alypius read on in the epistle to "Receive the person who is weak in faith" (Rom. 14:1). This Alypius applied to himself, and he was converted, as well. They went to tell Monica, who rejoiced at the news. Augustine declared that he no longer had the desire to marry or entertain worldly ambitions.
The story of Victorinus shows that, even this close to conversion, Augustine was still not free of earthly vanities. After reading it, the reader may feel tempted to use modern psychology and arrive at the conclusion that Augustine now had an example of "someone like him" (and, in fact, Victorinus was someone who Augustine at that point in his life could only aspire to be like) who had converted to Catholicism. The vague contempt for the faith that ran through the previous books is now gone. For the majority of his life, Augustine's mother Monica was his primary example of a Christian. The contemporary sources of the time tell us that Monica, like the majority of women at the time, was not an educated woman. It would be easy, therefore, for Augustine to dismiss (even if only subconsciously) his mother's fervent faith as the product of a mind less educated than his own. In Victorinus Augustine had a concrete example of a highly educated, successful, cultivated, and famous convert. Also, Victorinus was a native of Africa, like Augustine.
However, Augustine's snobbery, if it did indeed exist, was based on a very rigorous and informed kind of philosophical inquiry and a sincere desire to arrive at truth. Augustine did not join the Church out of hero worship, or out of a desire to be like a famous orator. His search for truth was very laborious and had caused him great pain. Augustine truly sought to discover the truth about God and the universe, and any other minor inducements to convert were only the nudges that helped him on his way. The major push came from Augustine's own inner desire for faith.
Augustine, it is clear, had no intention of doing anything halfway when it came to God. Perhaps part of the reason he reached the age of 31 before converting was that he knew that after he converted there would be no going back. If he was unmarried (as he was when he converted), it was likely he would remain so. He would give up most of his earthly pleasures and any worldly ambition. It was not a decision to be made lightly.
We can certainly admire Augustine for his integrity. There isn't any reason to suppose that his conversion wasn't completely sincere. In fact, if his writings are examined closely, it appears that his actual conversion began far before that day in the garden - perhaps with the release of his concubine. In hindsight, Augustine even says that it was quite obvious he was headed towards conversion. His struggles with the were not so much a question of "if" as a question of "when."
Augustine's conversion is quite climactic, and in it we can discern some of the hallmarks of a psychological break. He cannot make this decision without a violent physical reaction, which is followed by an ecstatic vision. Then he hears a voice directing him to a devotion, which converts his soul completely. If Augustine were not such a rational man certain marks of psychosis might be detected in this episode, but he recovers quickly and is immediately at peace with the decision.
The seven preceding books are roughly analogous to the classical seven ages of man. Augustine was nothing if not a good rhetor, and the symmetry between the ages and the various states of his spiritual life would have pleased his literary sensibilities. He makes the ages analogous to the states of his life not in a physical sense, but rather in a metaphorical one (his days as a student in Carthage, for example, are analogous to the "lover" age of man). This parallel would not have been lost on many of his contemporary readers, either. Augustine is a product of the ancient world, and he still lives within the framework of classical thought. Within that framework he becomes a Christian, but he never fully releases his Neoplatonist thought or his classical education.