This religion [Christianity] constitutes the single way for the liberation of all souls, for souls can be saved by no way but this. This is, if I may so speak, the King's highway which alone leads to a kingdom, not tottering on some temporal height, but secure on the firm foundations of eternity.And yet, Porphyry says that he knows of no religion that offers universal salvation. Which makes one have to wonder why he is so confident in the superiority of his own version of Platonism if it offers no more salvation than any other faith?
Yet, Christianity does offer such a way. (Augustine thinks Porphyry rejected it because he lived at a time when there was persecution of orthodoxy faith and rampant heresy dominating the church.) Christianity alone offers salvation to all men regardless of nation of origin. What was promised and symbolized in the Old Testament revelation to the nations of the world is actually fulfilled in the salvation accomplished by Christ in his Incarnation, Crucifixion, and Resurrection.
Even better, this salvation saves the whole person, not just the intellect (which would leave a need for another savior for the body, and another for the soul, and so on):
This way [the Gospel] purifies the whole man, preparing for immortality every mortal part of which man is composed... This way has never been lacking to the human race, whether at the time when these mysteries were being prophesied or when they were announced as already accomplished. Thus, no one has ever been liberated, nor is being liberated, nor ever will be liberated, except by this way.So Augustine believes that the last ten books have successfully refuted the pagan claims to truth and salvation, and now he is ready to talk about the two cities themselves as they actually exist in history.