Frodo at Sammath Naur

[Essex]

So when did he surrender to the Ring, if not at the Sammath Naur? Was it when he used it to threaten Gollum with death? Was it when he claimed it from Sam at the Tower of Cirith Ungol? Was it way back - had he unconsciously claimed it when he struggled to throw it into his own fire? When did he commit the 'sin' of putting his own desire first? The further back you place that transgression, the less excuse Frodo has for it.

I put it exactly at the point where Frodo said it. In other words where the Ring had pretty much taken control. Just before they climbed up Mount Doom.

I am almost in its power now. I could not give it up, and if you tried to take it I should go mad.

Frodo to Sam, Chapter 3, Book 6, Mount Doom.

Not Sin, (no doubt he desired the Ring, but that is not a sin), but as Frodo says himself, he was under the Power of the Ring.

Tolkien seems to say that Frodo was rewarded by The Authority for the mercy he had shown to Gollum by being 'saved' from his ultimate failure in claiming the Ring

Fine. Call it what you want then, the will of Illuvatar and not Fate, I don’t mind. It just proves my point that Mercy is what the events at Sammath Naur is about. Not failure, success or ‘Sin’.