For non-religious observers, it's not immediately clear why this matters. After all, if the pronouncements of the Church of England aren't relevant to you, why would it matter who's in charge of making them? In an age when 50 per cent of Britons say they have no religion, and 48 per cent of Anglicans say they never attend church, you could argue that a changing of the guard at Lambeth Palace is something of a non-event.
That's one perspective. But it could also be argued that the Archbishop of Canterbury, as leader of the country's established church, plays a key role in shaping England's religious discourse – and that, of course, includes the discourse around secularism and atheism. By most accounts, Rowan Williams has been a moderate, liberal leader of the Church – while he has criticised the New Atheists and spoken up for religion (he is Archbishop of Canterbury, after all), he has not been a leading voice in promoting the notion of "aggressive secularism", unlike his predecessor George Carey, who has led the way in arguing that Christians are being marginalised in modern Britain. It's not rare to hear atheists speak of their admiration for his intellect (he was widely praised, at least on the left, for his recent guest editorship of the New Statesman), and his debate with Richard Dawkins in Oxford last month demonstrated that he is a man with whom non-believers can engage constructively (at least on abstract philosophical matters).
In contrast, the man being tipped to replace Williams, the Archbishop of York John Sentamu, comes across as a less compromising figure. This isn't to say he's a George Carey or, to take a Catholic example, a Cardinal O'Brien, but he has spoken out against gay marriage and joined the war of words over the treatment of Christians in the workplace, suggesting that he could adopt a tougher line over secularism than Williams has. With this in mind, secularists who favour respectful co-existence between believers and non-believers could view Williams' retirement as an unfortunate development.
However, there is another way of looking at it. As more and more people in Britain turn away from religion, you could argue that the moderate, liberal outlook of Rowan Williams has helped to keep the Church of England attractive to the kind of loosely-Christian, occasional churchgoers that prevent it from fading into total obscurity. With a more uncompromising, socially conservative Archbishop in place, perhaps he Church will begin to seem a lot loss attractive to the "cultural Christians" of middle England. If you're the sort of secularist who would prefer to see an acceleration in the decline of religion, you could view the departure of the widely-admired Williams as a step in the right direction.
Those are just some quick thoughts on the matter, really – do share your own in the comments.