Although it's the only blow-by-blow theological commentary on Lord of the Rings that I'm aware of, I find myself constantly annoyed by Fleming Rutledge's The Battle for Middle-earth: Tolkien's Divine Design in The Lord of the Rings. There are the constant comparisons with the films (Rutledge seems unusually concerned about the casting, and even in one case, the costumes), there are the constant references to things that seem foreign to Tolkien (the CEO of the Herman Miller Company, Protestant hymns and prayers), and, most of all, the heavy-handed predestinationalism that is Rutledge's fundamental interpretive lens. He even has the gall to pen the following footnote:
There are technical names for these two differing interpretations of humanity's relation to God. In oversimplified terms, the position emphasizing the human decision ('free will') is called Pelagianism or Arminianism (semi-Pelagianism), after a British monk named Pelagius and a seventeenth-century Protestant called Jacobus Arminius. The other position, which gives priority to the divine will, was held by the apostle Paul. It is called Augustinianism after its defender Augustine of Hippo. Pelagianism is officially a heresy, but it has always been pervasive in the Church, never more so than in America where Free Will is a sacred doctrine. 
Of course, anticipating that it will be pointed out that Tolkien himself speaks of 'free will', Rutledge has already told us that the author 'underestimates the consistency of his own narrative', and 'has illustrated the dilemma of the bound will much more powerfully than he himself realized', managing to 'seem more "Protestant" than most Protestants'.  It would be wonderful to hear Tolkien's reaction to this!
But I'm afraid that to the extent that all of this is the case, that is, to the extent Tolkien really does illustrate 'the dilemma of the bound will' (nevermind the extent to which he realises it), it is likely because there is nothing specifically Protestant about the will being 'bound' or specifically Catholic about it being 'free'. Is it not both? Does any traditional Christian really believe that fallen human beings act without any sort of constraint or influence upon their wills? Does any believe that human beings are merely robots, being saved or damned merely due to God's 'programming' and without any personal moral responsibility whatsoever?
I recall last summer how much I appreciated it when I read the following passage in N.T. Wright's What Saint Paul Really Said:
Classically, this doctrine [of justification] ever since Augustine has been concerned with warding off some version or other of the Pelagian heresy. Different people have meant different things by that heresy, and the sharp-eyed have spotted it, sometimes, even in those who thought they were opposing it root and branch. I must insist, right away, that if you come upon anyone who genuinely thinks that they can fulfill Pelagius' programme, in whichever form or variation you like, you should gently but firmly set them right. There is simply no way that human beings can make themselves fit for the presence or salvation of God. What is more, I know of no serious theologian, Protestant, Catholic or Orthodox, who thinks otherwise; indeed, one of the best expositions of the Augustinian or Lutheran or Calvinist doctrine of justification I have ever heard was given by a Jesuit, Father Edward Yarnold, in an ecumenical meeting. If Pelagius survives at all today, it is at the level of popular secular moralism, which is in any case becoming harder and harder to find in the Western world. 
In this light, surely any reasonable person can see how much it begs the question simply to assert that St Paul is the firm opponent of anything that might be called 'Pelagianism', 'semi-Pelagianism', or 'Arminianism', or that St Augustine was purely and simply the defender of St Paul's theology. Nevertheless, this claim continues to be asserted–even the editor of the Ancient Christian Commentary on Scripture volume on Romans insists that of the Fathers, 'Only Augustine (354-430) was prepared to accept the logical consequences of Paul's teaching on this matter [of grace and free will], and this led to his famous quarrel with Pelagius.' 
Really? Only St Augustine actually accepted St Paul's teaching? Or perhaps only St Augustine, in his zeal to correct Pelagius, levelled out the paradox of grace and free will that all of the other Fathers saw, even in St Paul himself? Fr Georges Florovsky, for instance, has quoted one of my favourite passages from Romans–chapter 12, verse 2: 'Be not conformed to this age but be transformed by the renewing of the mind in order to prove [that you may prove] what [is] that good and well-pleasing and perfect will of God' (words in brackets are Florovsky's)–commenting:
Taken by itself and out of context this language could be misinterpreted as Pelagian, for here it is man who is transforming the mind, man who is commanded to activate the spiritual life. Such an interpretation is, of course, incorrect but it reveals what one can do to the totality of the theological thought of St Paul if one does not understand the balance, if one does not understand that his view is profoundly synergistic. Synergism does not mean that two energies are equal. Rather it means that there are two wills–one, the will of God which precedes, accompanies, and completes all that is good, positive, spiritual and redemptive, one that has willed that man have a spiritual will, a spiritual participation in the redemptive process; the other is the will of man which must respond, cooperate, 'co-suffer'. 
The funny thing is, of course, that even the demons understand this. As Screwtape writes:
Why [God] leaves room for their free will is the problem of problems, the secret behind the Enemy's nonsense about "Love". How it does so is no problem at all; for the Enemy does not foresee the humans making their free contributions in a future, but sees them doing so in His unbounded Now. And obviously to watch a man doing something is not to make him do it. 
Addendum: As it has been some time since I read Ralph Wood's excellent The Gospel According to Tolkien: Visions of the Kingdom in Middle-earth, I had forgotten that Wood too mentions this issue in Tolkien's work. He writes:
Tolkien is close to Paul and Augustine and their long train of followers who argue that real freedom is the liberty to choose and do the good, and that to do evil is to act unfreely, to exercise an enslaved will. These theologians all insist that God's grace enables our right response to it. For this venerable theological tradition, it is better to say that we are the product of the gifts we have graciously received rather than the sum of the decisions we have bravely made. 
It certainly sounds here as though Wood is trying to make the same point that Fleming Rutledge has so strongly emphasised. But perhaps it's just because I've met him a couple of times, read some of his other work, seen him speak, and just generally like the guy, but I'm inclined to note that Wood has put all of this much more carefully than Rutledge has. While he refers to the Augustinian approach as a 'venerable theological tradition', he does not say that all else is heresy, or that all of the other Fathers have balked at following St Paul. He says 'it is better to say' rather than 'we must say'.
This is not surprising when one considers, of course, that the context of Wood's comments is an analysis of the moral conflict between vices and virtues in the work. How can one speak of virtue at all if our choices are not really ours at all? Thus, notably, we find Wood later on striking a rather different chord:
God is utterly unlike Melkor and Sauron because he never coerces. We are never forced but always drawn to faith, as God grants us freedom from sin's compulsion. We are invited and persuaded to this act of total entrustment through the witness to the Gospel made by the church. 
Furthermore, I note later on that Wood strikes a very un-Augustinian chord indeed when he actually uses the word 'synergism' (à la Fr Florovsky) to describe the relationship between the divine will and those of the characters: 'The synergism of the holy and the human–as the divine and the hobbitic prove to be complimentary rather than contradictory–is disclosed most plainly when Frodo first encounters the Ring-wraiths.'  So, naturally, I find Wood to be an ally rather than an opponent on this question.
 Fleming Rutledge, The Battle for Middle-earth: Tolkien's Divine Design in The Lord of the Rings (Grand Rapids, MI: Eerdmans, 2004), pp. 67-8, n. 28.
 Ibid., p. 11.
 N.T. Wright, What Saint Paul Really Said: Was Paul of Tarsus the Real Founder of Christianity? (Grand Rapids, MI: Eerdmans, 1997), p. 116.
 Gerald Bray, 'Introduction to Romans', Romans, Vol. VI of Ancient Christian Commentary on Scripture: New Testament, ed. Gerald Bray (Downers Grove, IL: IVP, 1998), p. xix.
 Protopresbyter Georges Florovsky, 'The Ascetic Ideal & the New Testament: Reflections on the Critique of the Theology of the Reformation', Byzantine Ascetic & Spiritual Fathers, Vol. 10 in The Collected Works of Georges Florovsky, ed. Richard S. Haugh, tr. Raymond Miller, Anne-Marie Dollinger-Labriolle, & Helmut Wilhelm Schmiedel (Vaduz, Liechtenstein: Büchervertriebsanstalt, 1987), p. 34.
 C.S. Lewis, The Screwtape Letters with Screwtape Proposes a Toast (NY: Harper, 2001), p. 150.
 Ralph C. Wood, The Gospel According to Tolkien: Visions of the Kingdom in Middle-earth (Louisville, KY: Westminster John Knox, 2003), p. 70.
 Ibid., p. 119.
 Ibid., p. 122-3.