Malcolm Turnbull has staked his prime ministerial claim on explaining the economy seriously. To have his new Treasurer parroting three-word slogans and old discredited lines is not a good start, writes Mungo MacCallum.

As the political theatre goes, it can't get much more absurd than this: Tony Abbott and Bill Shorten have joined up in a unity ticket.

Both are convinced that nothing much will change after the ascension of Malcolm Turnbull: the rhetoric may be slicker, but the politics will linger on. And both Abbott and Shorten agree on something else, that this will be a good thing for each of them.

Abbott sees it in terms of self-justification: obviously just about everything he did in the last two years was spot on, so his successor will inevitably pursue the same formula to the next election and succeed, for which Abbott can take the lion's share of credit.

Shorten takes the contrary view: the Abbott legacy was toxic, but Turnbull either won't or can't change it and the conservatives in the party room will hold him to the path that must lead to their electoral doom and the two Liberal leaders will share the obloquy.

The majority of the public, of course, hope that this is a self-serving fantasy from both Abbott and Shorten; after all, the whole point of the exercise was to clear away the old dysfunction and make way for something - anything - more palatable. But it may be harder to achieve than it seemed at first, and it appears that many of Turnbull's ministers are seriously reluctant to embrace the future.

Like creatures emerging from the depths to take their first tentative steps on dry land, they have emerged confused and blinking in the fresh air, unsure what they should do next. Some of the newer, younger brigade seem ready and even eager to evolve, but many of the old guard are quite happy to either return to the water, or at best stay as amphibians.

Those who have retained their old portfolios are the most stubborn. Some simply see no need for change: they are doing pretty well in their previous jobs. This applies particularly to Foreign Minister Julie Bishop, Finance Minister Mathias Cormann and Trade Minister Andrew Robb. For them it will be business as usual.

In Immigration and Border Protection, Peter Dutton insists that nothing will vary, not a tittle - one tittle being the United Nations' Special Rapporteur on human rights, which will be welcome to come to Australia to enquire about Dutton's regime, but if they ask anyone about it the respondents may be put in jail. Unsurprisingly, this gracious invitation has been declined.

The Attorney-General George Brandis is still wallowing in the swamp, attempting to make sense of the morass he has devised to restrict civil liberties. In Environment Greg Hunt may be prepared to wriggle: it just could be that if circumstances develop, Australia's target of 26 to 28 per cent of emission reductions by 2030 could be increased - but not now, not yet. And in Health Sussan Ley was already mobile, and may well pick up the pace.

But the most important and disturbing signs come from the Treasurer, Scott Morrison. Morrison may have switched portfolios, but not the policies for which he has assumed responsibility. True, there is a new slogan: Jobs and Growth has been replaced by Work, Save, Invest. But what that actually means remains a mystery. Australians already do a fair bit of working, saving and investing; presumably the message is that we just have to do more. Second verse, same as the first, a little bit louder and a little bit worse.

And when it comes to the Government, not even the wording has changed; it is still Abbott-ese: Australia has a spending problem, not a revenue problem. As every rational economic commentator has pointed out, Australia has both and any attempt to fix one while dismissing the other is bound to fail.

And this encapsulates the real worry about Morrison. He wants to reduce complex issues to simplistic terms. This, apparently, is his idea of engaging in a conversation with the Australian people: to reduce everything to concepts so basic that there is no real room for discussion, let alone argument and debate.

It worked, more or less, in his previous career. His first job was in property policy, and then he moved to tourism, where he oversaw the "Where the bloody hell are you?" campaign with a dubious result.

As immigration minister, it was all about the slogan: Stop the Boats, at all costs, and never mind considerations of law, humanity or transparency. Even within Social Security, a more serious portfolio, Morrison was relentlessly focussed on clear and easily understood outcomes - indeed, he boasted about his direct approach.

But the Treasury is not like that; the economic issues facing the country are complex and nuanced. They cannot, or at least should not, be dumbed down into a couple of words suitable for focus groups, to be repeated endlessly until any vestige of sense has been beaten out of them. Turnbull has staked his claim to be Prime Minister on the need to explain the economy seriously and sensibly: to have his Treasurer parroting the same old discredited lines of the previous administration is not a good start.

The new leader himself continues to inspire hope and confidence. His big number on domestic violence has been very well received, and his speech at the inauguration of the memorial for war correspondents was masterful. To invoke the practitioners from Thucydides to Peter Greste was a reminder of how leaden Abbott had been on similar occasions. But those were the easy bits - unthreatening and uncontroversial. If Abbott and Shorten are to be proved wrong, and there is real sausage on the sizzle, some hard decisions cannot be avoided.

And above all, it will be the economy, stupid. Turnbull will be desperately hoping that his Treasurer can get up to speed, and soon. If ScoMo morphs into Slow-Mo, the great leap forward will quickly fall back into the primordial mire.

Mungo MacCallum is a political journalist and commentator.