"You are wise and powerful. Will you not take the Ring?" [Frodo asked.]
"No!" cried Gandalf, springing to his feet. "With that power I should have power too great and terrible. And over me the Ring would gain a power still greater and more deadly." His eyes flashed and his face was lit as by a fire within. "Do not tempt me! For I do not wish to become like the Dark Lord himself. Yet the way of the Ring to my heart is by pity, pity for weakness and the desire of strength to do good. Do not tempt me! I dare not take it, not even to keep it safe, unused. The wish to wield it would be too great for my strength. I shall have such need of it. Great perils lie before me."
-The Fellowship of the Ring, Book 1, Chapter 2
With apologies to anyone who thinks I should move on already, I'm going to revisit The Myth of a Christian Nation one more time. At the root of Gregory Boyd's argument for keeping the church out of politics is the concept of "power over" versus "power under." "Power over," of which political power is one type, is how the world attempts to solve its problems. "Power over" brings about a desired outcome by force, whether the coercion be physical, economic or psychological. The compliance of the other parties is all that matters, no matter how they actually feel about being forced to cooperate or what other consequences may result.
In stark contrast to that methodology, "power under" seeks to influence others in an entirely different way. Instead of lording over those who disagree with them, individuals following Christ's example humbly set aside their "rights" and their "moral authority" in order to serve others without expecting anything in return. Through acts of self-sacrificial love, practitioners of "power under" seek to slowly transform others from the inside out, even surrendering their own lives if necessary to bring about genuine change. It's a counterintuitive and seemingly illogical notion, but it's the example that Jesus set during his time on earth, and the method that enabled the early church to spread across the known world in the face of open hostility and persecution.
So what does that have to do with Gandalf? JRR Tolkien's conception of the One Ring fits very well as an analogy for the Church's perennial dilemma of whether to succumb to the temptation to use worldly power ("power over") to usher in the Kingdom of God. Tolkien, of course, made it clear that The Lord of the Rings wasn't meant to be taken as an allegory - not that that's stopped fans throughout the years from using it as one for everything from World War II to various presidencies to the Christian's spiritual life.
Nonetheless, Tolkien was writing mythology (in the best sense of the term), and as such various elements of the story can be seen as archetypes. Each generation faces its own epic challenges, and myths help us to view our own struggles from a different vantage point.
The best description of the One Ring that I've come across (and I wish I could remember where, so I could give credit where it's due) is that the Ring represents, not merely power, but coercive power - the power to dominate others and to force them to bend to your will.
Power in and of itself is not evil, it's simply an element of the world we live in. Many of the 'good' characters in The Lord of the Rings - Gandalf, Galadriel, Elrond, Tom Bombadil, etc. - were beings of considerable power, and at different times they used their power in opposition to the forces of evil. The difference between them and those on the side of evil is that they never used their power to override the free will of those around them.
Sauron's purpose in forging the One Ring was not merely power (which he already possessed), but the power to dominate. With it he transformed the nine human kings who wore the rings he had given them into the Nazgul, dark minions who existed only to serve him. And with it he sought to bend all of Middle Earth to his will.
With the power of the One Ring, Gandalf knew that he could overthrow Sauron himself, but in the process the Ring would have corrupted him and he would have become the very tyrant he sought to destroy. Each of the characters who came into contact with the Ring faced the temptation to take it for themselves, and in the end even Frodo found that he didn't have the willpower to relinquish the Ring.
Ultimately the Fellowship's quest succeeded only because Frodo chose to spare the life of Gollum, even though doing so imperiled his mission as much as it aided it, and even though he would have been fully justified in exercising what power he wielded to end Gollum's seemingly evil and miserable existence.
Had Frodo (or Gandalf, or Aragorn, or Galadriel, or Faramir, or even Elrond) succumbed to the temptation to exercise "power over" as a means to overcome evil, all would have ultimately been lost. Although the concept of "power under" only indirectly plays into the story, that is effectively what each of them chose when they rejected the easy solution of taking the Ring for themselves, even though it increased the risk to their own lives.
In the real world we already see the cascading effects of the American church's decision to take hold of and wield its own Ring by organizing as a political force, rather than choosing the more difficult path of unmaking the Ring by following the example of Christ. Even if the religious right ultimately succeeds in its quest to remake the United States into a 'Christian' nation, it will have done so at the cost of its own soul.
Government is a necessary institution in an imperfect world; without that impartial force to mediate disputes and protect individual citizens from predators (human or otherwise), civilization could not exist for very long. But as soon as the power of government is coopted to override free will by forcing others to conform to one group's definition of "goodness" - whether that coercion is used to punish "sexual sin," to impose "democracy" on unwilling nations or to confiscate the wealth of the rich in a quest to eradicate poverty - it becomes the very evil it set out to conquer.
By overriding the freedom of others in pursuit of some abstract ideal, we cast moral judgment on them, a job that only God Himself is qualified to undertake. By placing ourselves in God's role, we recommit the first sin from which all other sins flow: the sin of pride. If those we seek to judge are deserving of God's punishment, how much more do we make ourselves worthy of his wrath by usurping his authority?
When we take the power of the Ring for ourselves, Sauron wins even if he loses.