The Essence of the Tale

[Inziladun]

It's almost bedtime for me, but in brief I would say that the essence of LOTR to me is about duty and sacrifice.
Frodo is presented by Gandalf with the knowledge that the Ring must be destroyed, and that it came into Frodo's possession in order for him to be its guardian for an undetermined amount of time, and perhaps to take it himself to Mordor and destroy it.
Frodo takes the burden willingly, trusting Gandalf, not truly understanding at the first exactly what toll being the Ring-bearer would have on his body and spirit, Still, though, he could just as easily have denied the responsibility and remained a simple Shire Hobbit.
And then there's Sam, sticking with Frodo through it all out of love, yes, but also out of a sense of duty. He had a idea from the start of the quest that he had a job to do, a part to play, and nothing drew him away from it.

Gandalf's duty and overriding focus was the defeat of Sauron, and all his words and deeds were colored by that ideal.

So that's what I see in the book. It doesn't come through as much in the movies. Frodo seems to be rather harried and fearful instead of purposeful. Sam comes nearer the mark though,