"So let us forgive him" -- from the stairs of Cirith Ungol to the slopes of Mt Doom

The scene in The Two Towers where Gollum comes back down the stairs of Cirith Ungol to find Frodo and Sam asleep is remarkable for many reasons. Gollum, looking upon them, nearly repents of his decision to betray the hobbits to Shelob so he can get the Ring back. Sam, who has every reason to suspect Gollum is up to no good, treats Gollum harshly and Gollum responds in kind. Gollum's repentance is blighted, as Tolkien says in one of his letters (Letters #xxx p. xxx). The reader is left in the unaccustomed position of pitying Gollum and being disappointed in Sam. Gollum, who began the scene close to repentance, ends it with a renewed commitment to treachery. Sam, who began in anger and suspicion, ends in grudging remorse and apology. Frodo's attempt at conciliation fails utterly.

The scene is about two pages long. Gollum is the only character awake for the first half page. Sam wakes up and clashes with Gollum on the second half of that page. At the start of the second page Sam awakens Frodo. Just before Sam wakes up, the narrator draws attention to the fact that neither Frodo nor Sam could have witnessed Gollum's moment of near repentance, and explains what they would have seen if they had been awake. It is the moment that sets up the astonishing pathos of the scene:

Gollum looked at them. A strange expression passed over his lean hungry face. The gleam faded from his eyes, and they went dim and grey, old and tired. A spasm of pain seemed to twist him, and he turned away, peering back up towards the pass, shaking his head, as if engaged in some interior debate. Then he came back, and slowly putting out a trembling hand, very cautiously he touched Frodo’s knee – but almost the touch was a caress. For a fleeting moment, could one of the sleepers have seen him, they would have thought that they beheld an old weary hobbit, shrunken by the years that had carried him far beyond his time, beyond friends and kin, and the fields and streams of youth, an old starved pitiable thing.

(TT 4.viii.714). 

One of the most basic conceits of The Lord of the Rings is that Frodo largely wrote the book he gave to Sam to finish. Obviously, Frodo could have written what he saw after he woke up, and Sam could have told him about what had gone on after he woke up. Not only would Gollum have been unlikely to have filled Frodo and Sam in on what he was experiencing at the start of the scene, but after the end of this scene they see very little of Gollum for the rest of the book. So the narrator of the book isn't supposed to be omniscient, and Sam couldn't have seen more than an old weary looking Gollum touching Frodo's knee. Incredulity is a very weak argument, but it is very hard to believe that Tolkien both slipped up on the narrator's perspective and then called attention to that slip by pointing out that no one could have seen Gollum before Sam woke up. What we see here is one of the most thematically significant moments in the whole story, the moment in which the reader suddenly sees Gollum precisely as Bilbo saw him in The Hobbit, precisely as Gandalf thought Frodo needed to see him, though he at first refused to do so, and precisely as Sam sees him on the slopes of Mt Doom. With pity. If this happened by chance, it's chance-if-chance-you-call it.

But what is more important than how we might square the creation of this scene with the supposed narrator's limited perspective -- and I have my theories -- is how we read this moment in the thematic context of the book. We need to read it in the context of the movement from pity to mercy and thence to forgiveness. That forgiveness comes only after Gollum betrays them once more and is again shown mercy, this time by Sam who has finally suffered enough to realize what he saw when he opened his eyes on the stairs of Cirith Ungol. That mercy enabled the eucatastrophe in the Chambers of Fire. I think we may be able to fully understand the importance of what happens on the stairs if we read it in dialogue with Frodo's words after the Ring is destroyed:

‘Your poor hand!’ he said. ‘And I have nothing to bind it with, or comfort it. I would have spared him a whole hand of mine rather. But he’s gone now beyond recall, gone for ever.’ ‘

Yes,’ said Frodo. ‘But do you remember Gandalf’s words: Even Gollum may have something yet to do? But for him, Sam, I could not have destroyed the Ring. The Quest would have been in vain, even at the bitter end. So let us forgive him! For the Quest is achieved, and now all is over. I am glad you are here with me. Here at the end of all things, Sam.' 

(RK 6.iii.947)