I didn't think of myself as much of a monarchist. But the number of disappointed republicans currently putting frustrated pen to paper, not least in the paper for whom I write, the Guardian, has made me think again. They're caught between the manifest popularity of the royal wedding and their plea that we should not be infantilized by the monarchy but grow up into citizens. But they don't get it.

You don't grow up by ditching your parents. That's what adolescents try to do, as they stamp their feet and storm up to their bedrooms. You grow up by seeing them as ordinary individuals like you, though still your parents. Similarly with monarchy. Walter Bagehot was precisely wrong: it's because the daylight shines on the magic that the childish magic dissolves and the mature mystery can live. It looks like this is precisely what William and Katherine will achieve. We're telling their story as one of ordinary individuals in love who will also, one day, be king and queen. And both dimensions seem, in them, to fit together very well.

The mystery of the monarchy is that it holds all sorts of things for us that other political systems struggle to do. A modern monarchy speaks of the pre-political values necessary for democracy, values like charity and trust, and which the modern royal dignifies in his or her day job. These can't be voted in, and they are not rational. Though as we see in the countries struggling to become democracies because they don't have these civic virtues, they are absolutely vital.

The crown holds and represents transcendental ideals for us too, like justice, which the law mostly fails to achieve, but still must strive to achieve. The word 'crown' is doing as much work as the words 'prosecution' and 'service' in the CPS. And there's the symbolism. The monarch, like a married couple, makes a commitment for life, and whilst things will go wrong, the intention is still good as to live we must make a commitment to the future, whatever it may hold.

A republican will say that a president can do this things, along with the pageantry that surrounds the dignity of their office. Or that a country should be founded on explicit values, like liberty, fraternity and equality. Clearly, some countries opt for such alternative institutions - though I remember being persuaded that a monarchy has the upper hand when, after 9/11, it became almost impossible to criticize Bush without being taken as criticizing America too, because the political leader and the head of state were embodied in the same person. Similarly, a list of values will run into trouble when they conflict - as liberty and equality clearly do. A symbolic figure seems better able to hold together inevitable contradictions because they're symbolic not explicit.

That the monarch is born, not chosen, is therefore also a good thing. In a democracy, where political power rightly rests with elected representatives and the electorate, hereditary ensures the head of state is above the political. Their power is soft, in all the good things they stand for.