Today in St Paul’s Cathedral Sarah Mullally will be enthroned as the 133rd Bishop of London. For her, London, the Church of England and for the nation it is a momentous moment.

Ahead of her lies the task of leading and managing the largest and most diverse diocese in the country. She will become the third most senior Bishop in the nation’s Established Church, after the Archbishops of Canterbury and York, and one of the country’s most senior leaders. Her new Cathedral will be packed with well wishers and many others will be praying for the new Bishops success, for ahead of her lies the most enormous challenge – and opportunity.

The diocese she inherits is by the standards of most other parts of the Church of England in a relatively healthy condition. Across the country attendance at most churches is in sharp decline, especially in the north of England. Religious indifference is flourishing.

The proposed merger between the Church of England and the Methodists for example is gaining ground not out of mutual strength, but because of the growing weakness of the two institutions. London stands out as a relatively strong centre for the Church, but even here the warning lights are flashing around the number of those attending church and the number of priests for the years ahead. Today is not the day however to focus on the formidable challenges that lie ahead.

Much comment has focussed on the fact that she is the first woman to hold the job. This is, of course, noteworthy but in truth it is not as interesting as some of the other attributes she brings with her.

Dame Sarah Mullally is not a career priest. Her ecclesiastical, let alone episcopal, experience is, by historic standards, relatively slight. She has been a priest for barely sixteen years and a junior bishop for only three.

Before full time ministry Bishop Sarah forged a successful and impressive career in nursing and national leadership, serving as Chief Nursing Officer and the NHS’s director of patient experience for England. She brings to her new job a huge amount of experience of working in a large, resource strapped, decentralised, national organisation. Experience of Whitehall and politicians in a very sensitive area of national service delivery gives her a huge advantage over her fellow church leaders. Operating in the full glare of media attention is something she is used to.

Already this practical senior secular experience is evident. The new Bishop is at ease with social media, she is an avid tweeter. In the many personal visits and meetings she has held across the diocese she has demonstrated an easy warmth, a willingness to listen, and clear sense of unhurried purpose. Already there is a definite sense of the diocese warming to its new boss. For those already involved in Church life this all seems relatively reassuring, but of course the real task lies elsewhere.

For the vast majority of Londoners who are not involved or engaged with the church, this will not matter and will make no difference, but it is the London beyond the walls of the church that must be the main focus of the new Bishop’s attention in the months and years that lie ahead if the Church of England is to have a meaningful future beyond its institutional and established role.

In each generation, so the mantra goes, the church is called afresh to preach the Gospel. For Bishop Sarah the key to success will be to discern how to reapply the unique offering of the Church of England to her new diocese so it can reach out beyond the high walls of her numerous new churches and into the diverse communities of the country’s most cosmopolitan City.