You Are Not Alone
The Doctor goes so far in the other direction, in the end, that he allows himself -- the strongest, most beautiful being in existence, this thing that we're capable of, in those tiny moments of grace that are our tendency -- to be abused, mortified, shrunken and humiliated. Shaven and chained, like Aslan, because he knows that Martha, and humanity, will save him. In the end, it's the strength of the Doctor's sacrifice that saves the universe, and buys him the time. Can you imagine putting yourself at the mercy of stupid apes and knowing that they can do it on their own? It's the Third Testament all over again. The Doctor even gives up the notoriety and glory that it would bring him, when he admits it's best that nobody remember. In that lost year the Master was wiped away from him and his two hearts beat in tandem again, I'd say he earned his Jesus pose, because he found the truest expression of his power: to sacrifice it, and himself, to allow himself to be saved, caught in free-fall, by the people he's meant to lead and protect, to be debased by his evil twin, by the Jagrafess he always comes so close to becoming, by the wave of chaos he could be so easily. "Know your enemy": even Martha knows that there has to come a time when you give yourself up into your enemy's hands. And in the end, Martha forgives her Judas for putting love above survival. She gives her flowers.
But because the Master is a part of the Doctor -- the Faith part that takes a Neitzschean pleasure in its power -- he can't ever die completely. No second chances, no return to egg-form for another try. No second chances. The Master is just another Reinette, in a way -- somebody who's walked the Doctor so completely that the edges go fuzzy: "We are the same." I'd say that, beyond even the strength of sacrifice, the Doctor's knowing that this balance is forever going to be his problem is a truer expression of power; I also think that it's Martha who saved him from the Master's road, after Rose broke his dependent, human heart. Thinking you can really kill the Master? That's just a little boy, shooting at straw men, tears running down. The Doctor will always be scary, and he'll always need somebody to stop him, because that's how the Master happens: it's a natural consequence of power. That's "42" happening, forty-two minutes at a time, for nine hundred years and counting; ask the poor Family of Blood, or even the Weeping Angels, in their Schrödinger hell. It's the humanity in the Doctor, which Martha and all the Companions have forged and will continue to forge, that keep him on that path, for the most part. Life is balance and it's a constant working: grace is a wave that never breaks. They seem like two great faces, or a very large vase, but in fact they're just lines on paper, drawn in black and white, played on a stage by very tiny, very sexy men. It looks like this: