Islamic State's rallying call for its followers to kill all non-believers in the West is designed – as always – to terrorise, but the diatribe from its chief spokesman released on Monday is also revealing in betraying the weakness and fears of the terrorist group itself.

Abu Muhammad al-Adnani's speech is a twisted tour de force of malevolence, florid insults and apocalyptic threats.

It seeks to deliver retribution to the West, as punishment for the planned military campaign to degrade and destroy Islamic State, also known as IS or ISIL.

Whether they are soldiers, spies or civilians, kill a non-believer if you can, Adnani exhorts followers in Australia, Europe, Canada and the US.

If you don't have an improvised explosive device or a gun, he says, "smash his head with a rock; or slaughter him with a knife; or run him over with your car; or throw him down from a high place; or choke him; or poison him".

If that's not an option, burn the non-believers' crops, businesses or homes. Even then, "if you are unable to do so, then spit in his face".

As a call to arms, it's a scatter-gun approach, to say the least – and more than faintly ridiculous.

That's not to underplay the well-documented savagery of Islamic State or its success in capturing major cities and territory across Syria and Iraq.

The threats from Adnani will be, quite appropriately, be taken seriously by security agencies.

But Islamic State's focus has been on winning its military campaign – so far its capabilities to unleash a big terrorist attack in the West appear negligible. Adnani's threats do nothing to counter that view.

The alleged plot uncovered last week to kill on videotape random Australians snatched from the street was abhorrent and would have created widespread fear.

While disturbingly easy to implement, it was hardly in the same league as previous attacks planned here or al-Qaeda's spectacular mass casualty atrocities of a decade ago.

As he promises vengeance, Adnani also goads the West to invade – promising that it will bring only a long, bloody ground war and defeat.

Even so, there is a surprising admission of vulnerability.

"Oh Allah, you know our weakness. We have no way to deal with their airplanes," he says. "Oh Allah, you have placed them above us by their airplanes. Oh Allah, you know we have no power nor strength against their planes except through you."

The urgings for divine intervention are – as usual for violent Islamists – replete in the statement. The strong narrative is that Islamic State's gains in Syria and Iraq are proof theirs is a mission blessed and guided by Allah.

Routing Islamic State from Iraq and Syria – especially in Mosul and Raqqa, its two urban strongholds – will be difficult, and potentially disastrous if Muslim nations in the region aren't playing a significant and visible role in the coalition.

But Adnani's remarks support Prime Minister Tony Abbott's contention made in Parliament on Monday.

"It's ISIL's success on the battlefield, at least as much as its absolutism, that explains its perverse appeal.

"Stopping and reversing its advance … should also reduce its magnetism for people around the world."

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