A critter just asked me "Why is Trinidad going to save the world, stop the crusade, and fall in love with Castile?" (Ok, I added that last part, but I think it's important.) This lady just wrote a post called "Perfect Storm" which is guiding me to examine that question. It's been niggling at me ever since he asked me, not because I don't know but because I hadn't put it into words because there is no short answer.
When Trinidad was a kid, his Wiccan ecoterrorist parents suicide-bombed a store in Boulder, taking the lives of themselves, his little brother, and several others. Trinidad was subsequently adopted by an Episcopal priest and raised in the church. Even as an adult, he has only the most child-like view of why he was spared. He suffers from such latent anger, it was best to focus it into a career of controlled violence. All that, combined with utter loyalty to the priest who took him in (who is the Church, to Trinidad's mind) and resentment against Wicca, made him a perfect recruit for the Order of Archwardens. Throw in a martyr complex born of guilt and admiration for his parents' actions, folk hero status for his family among Indigos and Wiccans, and a church that subtly tells him again and again that he's a pariah, and you have a young man who is willing to lay down his life for his chosen religion. (I don't think it's such a leap that a kid whose parents did something would have a bit of a death wish. Such influence on children runs very deep.)
Trinidad lives caught between his chosen world and his past and there is one person on earth left who accepts him how he is, and that's Castile. That's why they fall in love, utter acceptance despite their differences.
Okay. Seem like enough? Your turn. Why is your protagonist The One?