(Prefatory note: though Taylor falls within the orbit of political theory, I've never read him in a systematic way. This is an attempt to pull a thread that is present, I believe, in The Sources of the Self and A Secular Age. It may already be well-discussed in the literature on Taylor. He may say something that expressly contradicts this elsewhere--if so, I'd appreciate a pointer. Forewarned is forearmed. Now I'll proceed.)
Jacob Levy reminds me, in the comments here, that while Walzer's "Dirty Hands" is a reminder of a certain kind of conflict between Protestant theology and politics, so is Thoreau's "Civil Disobedience," which, quoting, "is an appeal to clean hands and to a highly [Dissenting-]Protestant conscience. Having separated spheres, the Protestant may decide to reject the City of Man altogether and choose quietism and faith."
A Christian (though perhaps not only a Christian) faces a Scylla-and-Charybdis moment: one can fuse one's politics to one's religion, or else see them as fundamentally opposed. The first looks, on occasions, like the New Natural Law movement, which discovers that marriage is a fundamental good just in time to bring it to bear on policy debates. The second is the typical Stanley Hauerwas rejectionism, or, in a more moderate form, something like Walzer's Spheres of Justice. I assume that the dangers of too closely identifying politics and religion are obvious from the perspective of the religious believer: at a certain point, it's hard to tell which set of beliefs is animating the other. From a political point of view, too-close identification makes compromise difficult, and without compromise, not much can be done, whether you're a modus vivendi or a overlapping consensus (or deliberative democracy)-type. The problem with a dissociation of the two is less evident. The political arena loses something when a group of citizens opt themselves out of public debates, but from the perspective of those who drop out, that hardly matters. Here's where I want to segue to Taylor.
Recently, I finished reading The Sources of the Self with a colleague, and one of the topics we discussed was whether Taylor is affirming or rejecting modernity. Those who have read A Secular Age know that he spends a great deal of time arguing against what he calls the 'subtraction story,' where through a combination of material and sociological factors, especially the rise of science and rationalism, people cease to believe in God, and the possibility of secularism can finally be realized. It's not that he disputes the broad historical narrative; he just doesn't believe it's quite so simple as 'God drops out.'
The question I raised concerning Sources of the Self was whether it was not, in its own way, a subtraction story, a declinist narrative of What We Have Lost. He ends the book by playing with the image of mutilation, arguing that every viewpoint available to contemporary man involves some act of mutilation, a part of what it means to be human that must be sacrificed in order to live in the world as best one can. He holds out one possibility, though:
There is a large element of hope. It is a hope that I see implicit in Judaeo-Christian theism (however terrible the record of its adherents in history), and in its central promise of a divine affirmation of the human, more total than humans can ever hope to attain unaided. (p. 521)
The condition of contemporary man is, to put it another way, brokenness. Much, including much religion, counsels that individuals and communities accept that brokenness and attempt to put the pieces back together in the best manner they can. Taylor's alternative is a wholeness that comes through relationship with God, that's not simply wholeness, but something even more than we might otherwise expect. In this, he echos his earlier description of Augustine's relationship to God.
Augustine is removed from contemporary man not only by a millennium and a half (and then some), but also by many of those changes that have made the modern age possible. In some very real sense, we can't occupy the same world, or have the same thoughts, that he did. And yet:
None of us could ever grasp alone everything that is involved in our alienation from God and his action to bring us back. But there are a great many of us, scattered through history, who have had some powerful sense of some facet of this drama. Together we can live it more fully than any one of us could alone. Instead of reaching immediately for the weapons of polemic, we might better listen for a voice which we could never have assumed ourselves, whose tone might have been forever unknown to us if we hadn't strained to understand it. We will find that we have to extend this courtesy even to people who wouldn't have extended it to us... Our faith is not the acme of Christianity, but nor is it a degenerate version; it should rather be open to a conversation that ranges over the whole of the last 20 centuries (and even in some ways before). (A Secular Age, p. 754)
Something about the nature of Christianity makes it possible to bridge this divide, to pick up the threads of history and make sense of them, in a way that transcends the particular, and may do so systematically, rather than in fits and starts. His position is broadly ecumenicist, and so is likely to be rejected by many within the Christian community of which he is claiming himself to be a part. But again: he sees the possibility of wholeness, and won't accept unnecessary division.
The problem of sphere sovereignty in Protestant thinking, of approaches that try to separate religion and politics altogether, and reject the latter, is that they are premised on the kind of mutilation Taylor talks about at the end of Sources of the Self. The individual is both believer and citizen. Each leaves a residuum in the other, whether that's desirable or not, and separation at this level is just not possible.
To set up the last related observation from Taylor, I'd like to take a detour by way of James Poulos:
But the George Wills of the world persist in coming along and reminding us, as did Jesus and Nietzsche, that there is no earthly elimination of suffering, there is no way even to come close; that the best of us, the highest, may indeed be the ones who suffer most of all -- God or no God. This is the repugnant paradox that so outrages enemies of suffering and enthusiasts of proactive, coercive change toward solidarity...
And on a final note, it is because of this mysterious profound tension that politics must not take its cues from faith. The power unleashed is destructive of politics because the first good of politics is order, and the pressure of the tension I have described upsets the delicate balance required to keep politics itself from being nothing but a cruel and crude game of power.
In addition to this, Poulos criticizes the tendency of conservatives to let "The principle of friendship with the world's enemies of 'political suffering' gave way to the principle of solidarity with the world's objects of social suffering."
If one thinks that the first good of politics is order, the line of thought follows; if Machiavelli and Hobbes are the starting points, the possibilities of political and social life are limited--and as someone who, insomuch as they affiliate with any liberal tradition at all, has a soft spot for a Judith Shklar-style minimalism, the appeal is clear. But a few points are in order: it's easy, much too easy, to be glib about the suffering of others. The world does not suffer, at the moment, from an overabundance of Christian engagement in troublesome parts, whatever one thinks of 'Gersonism' and whether that accurately describes our foreign policy right now. The overwhelming tendency is to want to wash one's hands of, say, Africa, as a lost cause. (I'm not accusing Poulos of holding this view, and he makes clear that he doesn't have a lot of sympathy with a paleo viewpoint that is perfectly uninterested in suffering.)
There is an alternative view of politics, most familiar from liberalism, but I think compatible with a religious conservatism, that says the first good of politics is justice. One can spin that out too far, and many have, but the core idea is that we shouldn't let the impossibility of a perfect state of things blind us to what we can do right now to make things better:
But it is still true that the civilization which grew out of western Europe in modern times... has given an exceptional value to equality, rights, freedom, and the relief of suffering. We have somehow saddled ourselves with very high demands of universal justice and benevolence. Public opinion, concentrating on some popular or fashionable 'causes' and neglecting other equally crying needs and injustices, may apply these standards very selectively. Those defending the unconscionable always try to point this out, as though the existence of other blackguards somehow excuses them. South African apologists sound the alarm over communism, and defenders of communist regimes ask their critics why they don't attack military dictatorships. The premiss of all this special pleading is that our commitment really is to universal justice and well-being. Hence the unsettling ploy of accusing us of unjust selection, even when we attack what is obviously a flagrant injustice.
The counter-story to politics-as-order is that the language of justice in which all politics happens now is an inheritance from Christianity. Like all languages, it is open to abuse. Like all political orientations, it may be applied well or badly. Humility is always in order. But the Christian can, and should, have the conviction that a well-applied, deliberate effort in the direction of justice can be successful, and constitutes an acceptable bleeding over between the identities of citizen and believer.