In book five Augustine suddenly gets all theological (finally!). The main theme of the book is astrology ets. However, in V, 9 he discusses the possibility of prophecy with Cicero (who maintained that foreknowledge is impossible since it would make freedom of will impossible.
In V, 10 gets to answer the standard smartass question most theology teachers will face one day: How is it that God who is omnipotent cannot die or err.
For we do not make the life of God and the foreknowledge fo God subject to necessity if we say that it is 'necessary' for God to live forewer and to foreknow all things. By the same token, His power is not diminished when we say that He 'cannot' die or err. For this is impossible to him in such a way that, if it was possible, He would have less power. He is indeed rightly called omnipotent even though he cannot die or err. For He is called omnipotent because he does what he wills and does not undergo what He does not will: if this were not so, He certainly would not be omnipotent.Of course, this makes it dificult for Augustine to approach the problem of theodicy, but that question is not treated here. This is to me very much not the Eastern concept of pantokrator that might be defined as to have the ability to do what one wills, but perpaps not always not undergo what one does not will.