Gosh, you guys are making these polls harder and harder! It was such a hard decision. All those instances, and little vignettes from the LOTr started to run through my head, but of course, I couldn't decide which one was MOST important, because without any of them, the mission would not have succeeded.
but in the end, I chose temptation and resistance because the one central object in this trilogy is the Ring, and what does it do? It tempts. It tempted Gandalf, Saruman, Galadriel, Boromir, Denethor, Faramir, Aragorn, Frodo, Gollum, and back in time to Isildur, to name a few. A very central theme that recurrs throughout the LOTR is the idea that power corrupts. Those that resisted the Ring's temptations were good and pure and lordly (Aragorn, Faramir, Galadriel) and those who succumbed to it were not necessarily bad, but they were not as "pure" of heart and had too much ambition (Boromir, Denethor, Saruman).
And then, you have the whole Nine Ringwraiths business. How did those hovering pieces of ugly black cloth come to be what they were? Well, surprise, surprise, they were tempted by Sauron!
Now, after typing all this, I feel as if I've made the right choice, but still, you can't really ignore some of the other options on this poll. I mean, all of them count for a great part of the book, and I guess that's the wonder of Tolkien's mythology: you can learn so many lessons from just one great story.