Elijah lamented his fate, claiming to be the only one who had remained faithful to God in all of Israel? God corrected Elijah. There were a few more left, some thousands in fact. Elijah did not know them. They, apparently, had not sought out Elijah. He, though, was not alone. Even in a time when enormous governmental and cultural pressures pushed most people toward idolatry, a significant minority remained faithful.
That kind of story is the only answer I can provide to your question ("How do we hold to the truth," etc.). Some always have, some do so even now, and some always will. When all is said and done, evil wins the field for only a day, and even then it's victory is never complete.
I might add that John's Revelation is not about the end of the world per se but instead about the possibilty of faithfulness under the most trying circumstances. The living faithful in Revelation, by the way, are never called into battle. Their only job is to remain faithful to Jesus. The final defeat of evil is left to God. Of course, faithfulness might, in fact will, lead to trouble. One's witness, though, does not involve might and arms but instead a willingness to suffer and even die for the sake of fidelity to the Lord.
Mao said all power comes from the muzzle of a gun. I say that's but one kind of power, and far from the most effective over the long term. The power of love coupled with a willingness to suffer the consequences startles us. It may change us, and it always has within it the potential to change everything. This, of course, amounts to a faith statement. So be it. It's the one I choose to believe.
It's a faith statement that keeps cropping up, though. Jesus certainly thought so. Augustine, in his better moments, does the same. St. Francis makes this the ordering center of his life and work. Paul starts to get it, especially as he ages and reflects more deeply on the intent of Jesus. The perspective lies at the heart of some of the most loved contemporary literature. You'll find it in Tolkein. It seems to me to at the heart of much of what E. B. White had to say. As for the Harry Potter stories, the power of love relative to that of almost unthinkable, unstoppable evil is the central question addressed.
Finally, I think love takes root and grows in individuals. Jesus, indeed, directed his teaching, his way of life, at individuals. His community will be composed of individuals, each one of whom makes (and remakes, over and over) the decision to accept the love of God and to become in due measure an living embodiment of that love. All else--theology, actions, institutions, corporate worship, ethics, etc--becomes a running commentary or expression of this central reality.
There, well, both of us have had quite a run over the past few posts. Let me know if you are ready to press on.