I always wondered if Saints did not come in pairs. In this case they did. Augustine came under the influence of Bishop Ambrose. He was touched by his preaching. Here is a time line gleaned from Augustine's book Confessions:
He studies at Carthage, converts to Manichaeism and continues his ndulgences in lust between ages 16 and 19.
His loss of a friend and his studies in Aristotle and the fit and the fair between 20 and 29. Augustine is overcome with grief after his friend dies in his absence. Things he used to love become hateful to him because everything reminds him of what was lost. He concludes that any time one loves something not in God, one is bound to feel such loss. Augustine then suggests that he began to love his life of sorrow more than his fallen friend.
His movement away from Manichaeism under the influence of St. Ambrose in Milan at 29. Augustine begins to understand that things said simply can be true, while things put eloquently may be lacking in substance. He is unimpressed with the substance of Manichaeism, but has not yet found something to replace it. He feels a sense of resigned acceptance to these fables as he has not yet formed a spiritual core to prove their falsity.
His movement towards Christianity under the influence of St. Ambrose at 30. He is taken aback by Ambrose's kindness but still does not understand the substance of his teachings.
His rejection of Manichee dualism and the Neoplatonist view of God at 31. He struggles to understand the Christian God.
His continued inner turmoil on whether to convert to Christianity at 32. Two of his friends, Simplicianus and Ponticianus, tell Augustine stories about others converting. While reflecting in a garden, he hears a child's voice chanting "take up and read." Augustine picks up a Bible and reads the passage it opens to, Romans 13:13-14. His friend Alypius follows his example. Finally, Augustine decides to convert to Christianity.
His baptism done by Ambrose at 33, the death of his mother Saint Monica, the death of his friends Nebridius and Vecundus, and his abandonment of his studies of rhetoric.