Cicero was successful in refuting astrology, and for that we may praise him.
And yet, Augustine says, he went too far. Cicero overcorrected in his refutation of astrology to the point where he functionally argued against Divine foreknowledge. As Christians, if we are given a choice between determinists/fatalists and denying that God knows the future, "they are far more tolerable who assert the fatal influence of the stars than they who deny the foreknowledge of future events."
But why would someone as sharp as Cicero fall into this error? Because, according to Augustine, Cicero was trying to preserve the doctrine of human free will. Cicero makes arguments that we hear far too often even from Christians today--that if God knows the future, then it must be determined and we consequently cannot be held morally accountable for our actions since we have no choice in the matter: we have no free will. (I subject I've treated on another blog.) This in turn creates according to Cicero a morally monstrous universe where men may sin with impunity since they cannot reasonably be judged for actions which have been pre-determined beyond their control. Even Cicero's attempt not to fall into atheism and impiety falls flat when he tries (and fails) to find some kind of balance between fate and foreknowledge. An impersonal fate set in stone can never balance against human free will, the two will end in an unresolveable logical and moral conflict.
The only way to truly reconcile these two seemingly conflicting beliefs is through the Christian doctrines of Providence and Predestination. Augustine begins his exposition: "Now, against the sacrilegious and impious darings of reason, we assert both that God knows all things before they come to pass, and that we do by our free will whatsoever we know and feel to be done by us only because we will it."
In other words, at the same time God is sovereign over everything that happens and we are responsible moral agents. The sovereignty of God is, according to Augustine, such that "it does not follow that, though there is for God a certain order of all causes, there must therefore be nothing depending on the free exercise of our own wills, for our wills themselves are included in that order of causes which is certain to God, and is embraced by His foreknowledge, for human wills are also causes of human actions; and He who foreknew all the causes of things would certainly among those causes not have been ignorant of our wills."
In other words, God's sovereignty overlaps our will and governs all of existence without impeding our moral accountability. This in no way lessens the authority or sovereignty of God, He remains the ultimate source of all life and action in the universe:
The spirit of life, therefore, which quickens all things, and is the creator of every body, and of every created spirit, is God Himself, the uncreated spirit. In His supreme will resides the power which acts on the wills of all created spirits, helping the good, judging the evil, controlling all, granting power to some, not granting it to others. For, as He is the creator of all natures, so also is He the bestower of all powers, not of all wills; for wicked wills are not from Him, being contrary to nature, which is from Him. As to bodies, they are more subject to wills: some to our wills, by which I mean the wills of all living mortal creatures, but more to the wills of men than of beasts. But all of them are most of all subject to the will of God, to whom all wills also are subject, since they have no power except what He has bestowed upon them. The cause of things, therefore, which makes but is not made, is God; but all other causes both make and are made.God is the source of all life and action in the universe, everything we do as living beings is tied directly into His creative power. This is no cold Stoic view of fate, but rather is a personal and involved God pouring life into creation and directing its flow and development according to His own wisdom, goodness, will, and (though it's not mentioned here, we know that Augustine believed it) love. God's determination, His predestination, of existence is not one of a solid and stony future that is unalterable in content (though it is unchangeable). It involves "helping the good, judging the evil, controlling all, granting power to some, not granting it to others." God's personal hand is at work guiding, judging, shaping, pouring out grace and mercy and wrath and all of His character on a world that refuses to acknowledge His existence. In doing so, He does not become tainted by the wicked wills of His creatures but rather directs them to His own ends despite themselves. God commands evil without causing it, and in doing so reveals Himself and His creative power to all of creation.
As I said above, only the Christian understanding of Providence and Predestination can ever truly reconcile the sovereignty of God with human free will, and the only way it can do that is by remembering the personal nature of God's involvement in creation. At no point may we elevate the human will above Divine sovereignty, but also at no point may we de-personalize Divine sovereignty so that fits the caricature of a harsh fate. We must neither picture God tied up in the corner weeping while human beings shape creation with their wicked wills; nor must we picture a harsh and uncaring God who does what He wishes with no love for what He has made. Both must be held in Biblical balance, and Augustine is one of the masters at doing so.
The conclusion of all of this is that the pagan ideas of fate are simply false, but not more false than Cicero's attempt to elevate free will above Divine sovereignty. To be sure, Augustine's ideas are rough hewn. But then, he is just one link in a chain of theological development that begins with Scripture, is articulated by Augustine, expanded on by Gottschalk and Aquinas, purified by Calvin, and finally refined by Edwards. Not of course that we're at the end of the chain, that will only come when the book of predestined history is finally closed with the gathering of the saints and return of Christ in triumph.