Will There Be Free Will in Heaven??

I just finished the last five pages of the City of God (Hurray!!!)  and came across Augustine's answer to a philosophical question that has always puzzled and intrigued me.  If there will be no sin in heaven, and no possibility of sinning and rebelling against God as Lucifer and the demons did, and as the first humans did in Eden, how could there possibly be free will in the New Jerusalem?  Here's how Augustine navigates this issue:

"Also [in the City of God] they will then no longer be able to take delight in sin.  This does not mean, however, that they will have no free will.  On the contrary, it will be all the more free, because set free from delight in sinning to take a constant delight in not sinning.  For when man was created righteous, the first freedom of will that he was given consisted in an ability not to sin [posse non peccare] but also in an ability to sin [posse peccare]. But this last freedom of will will be greater, in that it will consist in not being able to sin [non posse peccare].  This, however, will not be a natural possibility, but a gift from God.  For it is one thing to be God, and another to be a partaker of God:  God is by nature unable too sin; but he who partakes of God's nature receives the impossibility of sinning only as a gift from God.   Moreover, in the divine gift of free will there was to be observed a gradation such that man should first receive a free will by which he was able not to sin, and finally a free will by which he was not able to sin:  the former being given to man in a state of probation, and the latter to him in a state of reward.  But because human nature sinned when it had the power to sin, it is redeemed by a more abundant gift of grace so that it may be led to that state of freedom in which it cannot sin."  (XXII. 30)

Augustine's answer here about human freedom in the Eschaton solves another tricky issue related to Adam's Fall in the Garden.  If God has foreordained the future such that Adam's decent into sin is an integral part of His eternal decree, how is God not the author of sin??  In a real sense this is the big, uncomfortable question that makes most Calvinists squirm when pressed to give an answer.  Augustine's answer here is that Adam in the Garden had the ability not to sin [posse non peccare] which entails full freedom of the will, but for some reason unknown to us, God in his sovereignty chose to withhold his grace from Adam. (a passive, rather than an active response on God's part)  According to Augustine's logic, the restored order in the Eschaton will be even better than the Garden of Eden, because at that time God will extend grace to all of the elect so that they will not be able to sin [non posse peccare].  Augustine therefore shifts the issue from any blasphemous notion we may have of a defect in the human will placed there by God, to the giving/ withholding of a divine "gift" of grace which guarantees that the will chooses what is Good.  Since God is under no obligation to give grace to even a single person (grace by definition is 'unmerited favour'), withholding this gift from Adam even prior to the first sin does not implicate God in that first terrible act of rebellion.  Adam used his own free will to rebel against God, and God, acting in accordance with His eternal decree, did not prevent Adam from sinning even though He could have done so.  Quite an ingenious solution to a very difficult theological problem!