The following is a quote from Tom Shippey's J.R.R. Tolkien: Author of the Century, "Chapter III, The Lord of the Rings (2): Concepts of Evil." Through an examination of Tolkien's use of wraith and shadow combined with Twentieth Century concepts of addiction and psychological persuasion, Tolkien compares and contrasts two view of evil which have been discussed for many centuries, and which are supposedly mutually exclusive.
One is the Christian view of Boethius, that evil has no real existence, being merely spoiled goodness. The other is Manichaean, that evil is very real and must be opposed by the good. Both have things to commend themselves to our consideration, and Tolkien emphasizes first the one, then the other, in his presentation of the power of evil in the world. These come to a climax in the scene in the Sammath Naur. Shippey picks up the argument:
At that moment, standing on the very edge of the Crack of Doom, Frodo gives up. His words are:
'I have come . . . But I do not choose now to do what I came to do. I will not do this deed. The Ring is mine.'
With that he puts it on for the sixth and final time. it is a vital question to know whether Frodo does this because he has been made to, or whether he has succumbed to inner temptation. What he says suggests the latter, for he appears to be claiming responsibility very firmly: 'I will not . . . the Ring is mine.' Against that, there has been the increasing sense of reaching a centre of power, where all other powers are 'subdued.' If that is the case, Frodo could no more help himself than if he had been swept away by a river, or buried in a landslide. It is also interesting that Frodo does not say, 'I choose not to do,' but 'I do not choose to do'. Maybe (and Tolkien was a professor of language) the choice of words is absolutely accurate. Frodo does not choose; the choice is made for him.
The question becomes an academic one, of course, in that the result is achieved by Gollum, fulfilling Frodo's own words a few moments before, 'If you touch me ever again, you shall be cast yourself into the Fire of Doom'. But Tolkien was an academic, and academics often see importance in academic issues where others do not. Is Frodo guilty? Has he given in to temptation? Or just been overpowered by evil? If one puts the questions like that, there is a surprising and ominous echo to them, which suggest that this whole debate between 'Boethian' and 'Manichaean' views, far from being one between orthodoxy and heresy, is at the absolute heart of the Christian religion itself. The Lord's Prayer, which in Tolkien's day everyone knew, and which most English-speakers know even yet, contains seven clauses or requests, and of these the sixth and seventh are:
Lead us not into temptation,
but deliver us from evil.
Are these variants of each other, saying the same thing? Or (much more likely) do they have different but complementary intentions, the first asking God to keep us safe from ourselves (the Boethian source of sin), the second asking for protection from outside (the source of evil in a Manichaean universe)? If the latter is the case, then Tolkien's double or ambiguous view of evil is not a flirtation with heresy after all, but expresses a truth about the nature of the universe denied to the philosopher Boethius, and possibly even to the rationalist Lewis.