For me personally, the most powerful metaphor in The Lord of The Rings concerns the ring itself. The ring seems to me to be illustrative of our ongoing struggle with sin. It is this object that seems to promise grand power and a level of personal gain not to be equaled. And to some degree that is true. Those who hold the ring do hold a sort of power, a step up on the competition, provided of course by the one whose power backs the ring, by Sauron. Unfortunately, Sauron's intentions are for his own gain, and the one who would wear the ring hoping to obtain much for themselves, only end up being drained of more and more of their soul. So too it is with sin. Sin always promises us something we think we will benefit by, but in the end it only robs us (and those we interact with in the course of our sin). It literally drains the life out of us.