You Are Not Alone
But it's really just two dots and a curve. It was you who made it real. The Doctor and the Master in conflict was the two sides of a God, fighting for a position from which to perceive his relationship to humanity. The Doctor, who doctors, and the Master, who masters. The open hand and the closed fist. Mercy and Judgment. Either the Last of the Timelords is so in charge of humanity that he can put it into a paradoxical self-destructive loop, like toys, for his own enjoyment and mad quest for war...or he can sacrifice his power, authority, and pride, and let humanity save him. It's the smart kind of faith again, where stories and songs bring you strength from strange places; it's the kind where you realize you can save yourself.
Imperfect execution, I'll admit, but the elements are there. That last is why I don't have a problem with the Messiah bullshit, or the glowing Tinkerbell Jesusiness of it all: it's not about the Doctor becoming super-powerful and not learning his lesson, but about the moment just before that, about that forgotten year, when he realized that there was nothing to be lost in handing humanity the reins. He knows that grace operates for him too, and that, in jumping, he has a chance to save everybody, even the Master. Because the Master is not a foe in the classic sense: he's a brother, someone with whom the Doctor's relationship verges on the romantic, and a necessary element of both the universe and the Doctor himself. When the Face of Boe says, "You are not alone," it could be a wish: the Master is just the plutonium inside.
If the Master in this story is one-half of a Timelord, then John Simm is the perfect person to place opposite Tennant. From the Martha/Lucy, light/dark Companion stuff, to the childish ADD, he's a match physically and energetically as much as philosophically or psychologically, as a character. It makes me wonder what an Eccleston-era Master could possibly have been like; Severus Snape is my best guess. Saxon even takes on a warped version the burden of Ten's loneliness, most especially in his need for Ten to hear the drums of war. All along, he's been convinced that it's a Timelord thing, and that Ten's just denying him out of some kind of pique. If the drums are his alone, then he's a madman: he is evil for its own sake, destruction uninformed by any directing or rational force. Which may or may not be true, but Saxon's not allowed to think that: evil can't look at itself. However, if Ten can hear them too, they'll be united. The conflict has to be resolved either way, because the point of stories is to resolve conflicts, but if the Master is on top when that happens, we won't have any more stories. And the Doctor's never heard the drums: in this case (alone, perhaps) the Master is a tree without a forest. "It's just you," the Doctor says. The Doctor is the true Timelord, and the drums are just a sign of the Master's illness. And the Doctor weeps for him, and so did you, and don't try to deny it.