It might seem odd to defend the Foreign and Commonwealth Office from the Foreign Secretary. But if I had been a British ambassador sitting yesterday listening to David Miliband, in his address to the annual gathering of Britain's 160 ambassadors, I would have felt discouraged and baffled, if not outright angry, at his fleeting acknowledgement of the organisation's present skills in his call to get ready for tomorrow.

You can't fault Mr Miliband on his enthusiasm for trying to frame the future in words. The concepts click together in endless permutations, like verbal Lego — globalisation, the Asian century, asymmetric warfare, strategic priorities. To his credit, he has used the post to set out the principles that he believes should drive Britain's foreign policy: that it should urge action on climate change; advocate democracy; and encourage a notion of sovereignty that means that if states treat their citizens appallingly, they will not escape attention by others. Margaret Beckett, his predecessor, appeared really moved only by climate change; Jack Straw, before her, preferred deals to abstractions.

There is, though, a point at which these torrents of concepts become dislocated from the business of government; when Mr Miliband begins to seem like the leader of the most ebullient think-tank in town rather than a senior minister. “I prefer to describe our role in the world as a global hub,” he said. “We need to change where we are — our global footprint needs to keep pace with our new priorities.”

Yesterday he put so much weight on new global challenges that the old-fashioned notion of national interest slithered away. In urging radical change on the Foreign Office, he has a case that threats will change. Yet today's problems (Iran, Kenya, Kosovo) have been tests of traditional skills of getting a deal to stick. He ended with a call for Britain to “look outward” and not withdraw but it would be only human, listening to this excited sermon, to take a small step backwards from the Foreign Secretary, if not the world.

He did make some important and practical points. The Foreign Office needs to put more people in rougher parts of the world, and fewer in Europe. It will be a less comfortable place to work, particularly for those with families. The Foreign Office, the Ministry of Defence and the Department for International Development should work more closely together. That is a polite way of touching on a serious issue: whether the development ministry can be brought into the service of foreign policy aims. The Department for International Development, part of the Foreign Office until 1997, now has a budget several times greater. Under its first Secretary of State, Clare Short, who resigned from the Cabinet in 2003 over Iraq, it kept fiercely separate from that war, preferring to focus on Africa and causes separate from British interests. But Afghanistan and Iraq are high in Britain's priorities, and yet the department's culture and skills have kept it on the outside.

Mr Miliband is also right to observe that as ministers in different countries now often talk directly to each other, it erodes the ambassador's role. His response is that “our added value comes in three core competencies”. The old Foreign Office skill of clear prose is not to be one of them, it seems; gibes aside, this is where his speech bubbles away with itself, and it is worth reproducing (almost) in full. “First, we should understand foreign countries' interests, power structures and culture better than anyone else. Second, we should have unparalleled networks that enable us to influence a country's position from the bottom up as well as the top down. Third ... the Foreign Office should have the overview of how to prosecute cross-governmental priorities.”

You know what he means, sort of, but the prescription is unforgivably vague. When he does risk precision, in a remark that would sound menacing from any manager, he argues that “across the office, we need a better mix between people who are good at criticism and deconstruction, and those good at creative solutions and synthesis”. Who in yesterday's audience would not interpret that as a dig that the Foreign Office has too many of the former? But if he wants to include himself among the latter, he needs to speak in a language clear enough to be understood, and actually to say what he intends to do.

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