Augustine has shown that all we need is happiness ("Felicity"), which is not a goddess but which comes only through the worship of the true God. What we have to do now is explore why on earth God would give the Romans such a powerful and long-lasting empire.
So why did the Romans achieve such worldly power? "The cause, then, of the greatness of the Roman empire is neither fortuitous nor fatal, according to the judgment or opinion of those who call those things fortuitous which either have no causes, or such causes as do not proceed from some intelligible order, and those things fatal which happen independently of the will of God and man, by the necessity of a certain order. In a word, human kingdoms are established by divine providence. And if any one attributes their existence to fate, because he calls the will or the power of God itself by the name of fate, let him keep his opinion, but correct his language. "
In this chapter, Augustine gives us an extended discussion of the Christian view of fate and astrology. Do the stars govern--or even reflect--human affairs? Might we even, if we're at least trying to be Christians here, say that God has coordinated the positions of the stars with human affairs? "They, however, who make the position of the stars depend on the divine will, and in a manner decree what character each man shall have, and what good or evil shall happen to him, if they think that these same stars have that power conferred upon them by the supreme power of God, in order that they may determine these things according to their will, do a great injury to the celestial sphere..."
I suspect that in the 21st century we're tempted to dismiss this idea as a relic of the distant past, or at least to allegorize the language so that it's a more general response to naturalism or scientific law or some such. But it's useful to remember that there are people today who still need to hear that the stars do not determine or reflect human existence. At least where I live, the local paper still prints a horoscope, there are still fortune tellers who prey on the superstitious by promising to read the stars, and how many of us have friends who believe in signs and portents in the natural world?
Augustine's reminder is useful: God alone is sovereign over all of creation, and He does not delegate that responsibility.
In fact, we can even apply some limited scientific reasoning to the question of fate and astrology (at least such as existed in Augustine's time). If the stars govern our lives, then we should sure expect twins to have virtually identical lifestyles. And yet we all know by observation that such is not the case.