John McDonnell, for so long the Robespierre of the left, is on a mission to reinvent himself. Labour's new shadow chancellor began his first conference address by promising that it would not be a "rant". And it wasn't. The man who has previously called for the IRA to be honoured, joked about assassinating Margaret Thatcher and declared of Tory minister Esther McVey, "Why aren't we lynching the bastard?", eschewed such violent rhetoric.

Instead, he offered an often wonkish account of how he aspired to change "the economic discourse in this country". There were unlikely whoops and cheers from delegates as he announced the membership of his Economic Advisory Committee ("including Joseph Stiglitz, Thomas Piketty, Professor Mariana Mazzucato, Simon Wren Lewis, Ann Pettifor and former member of the Bank of England Monetary Committee, David Blanchflower") and promised that Bob Kerslake, the former head of the civil service, would lead a review into "the operation of the Treasury itself." Setting out his defining dividing line with the Conservatives and his predecessor, he vowed to "oppose the cuts to our public services". But seeking to redefine the terms of debate, he pledged that Labour would make its own "cuts" - but to the corporate welfare system, not "the number of police officers on our streets or nurses in our hospitals or teachers in our classrooms."

When Ed Miliband delivered his conference speech last year, he was castigated for failing to mention the deficit. It was a charge that McDonnell quickly insulated himself from. Labour, he vowed, would "tackle the deficit" through "aggressive" action to "force people like Starbucks, Vodafone, Amazon and Google and all the others to pay their fair share of taxes." But there was no explanation of how. Combined with the promise of "people's quantitative easing" in times of anaemic growth, the impression that Labour relies on a magic money tree risks only being reinforced. McDonnell assured delegates that Labour would not fall into the "trap" set by George Osborne in the form of his fiscal charter (which commits the government to achieving an overall surplus by 2020). But there was no clarity today on how the party would vote on the document. McDonnell moved delegates with the old cry that "another world is possible" and his vow to provide 100,000 homeless children with "a decent and secure home in which to live." But again, just how the new world would be born was unclear.

It was the political, rather than the economic, content of the speech that was perhaps most notable. The loudest applause from delegates came when McDonnell appealed to those MPs who refused to serve under Jeremy Corbyn to "come back and help us succeed". The appeal was offered "in the spirit of solidarity" but to many on the outside, as one MP told me, "it sounded like a threat". Corbyn, by contrast, told me that "All Labour MPs have got a role to play, all Labour MPs have got a contribution to make" when I interviewed him. Those moderates who chose to take shadow cabinet posts did so in part because they fear being blamed if the new leadership fails. McDonnell's call for all MPs to "help us succeed" heightens the chance that those on the outside will be.