The beheading of US journalist Steven Sotloff caught the West's attention, as was intended by his executioner. But the fact that Mr Sotloff - abducted in Syria in 2013 - was Jewish has attracted little discussion.

That may have been partly due to the efforts made to hide his background over fears that such information would make his release less likely, or lead to extra cruelty from his captors.

As soon as his death was confirmed, a few facts trickled out: he had Israeli citizenship, his grandparents survived the Holocaust and his mother, Shirley, is a teacher at a Jewish school in Miami.

We may never know whether Mr Sotloff's captors knew he was Jewish. A fellow hostage has claimed that he successfully kept his Judaism a secret. On the other hand, reports that he observed the High Holy Days, and prayed toward Jerusalem by observing the direction in which his Muslim captors prayed, suggest they could well have had an inkling.

But if Islamic State knew, what of the silence? There were no diatribes against Israel, no rants about Jews, either in the final speech from jihadi John himself or in any of the related propaganda from the terror outfit.

Contrast that with the 2002 kidnapping and beheading of Daniel Pearl by al-Qaeda in Pakistan. Mr Pearl was kidnapped "especially because he was American and Jewish" said the French philosopher Bernard-Henri Levy, who researched the Pearl case.

However, to conclude that Islamic State is somehow a more mature ideological grouping than al-Qaeda would be a grave mistake. What this episode may show is that Islamic State has a more sophisticated grasp of media manipulation, and a reluctance at this early stage of the new caliphate's existence to provoke Israel's wrath.

With the IDF and the al-Qaeda offshoot Al-Nusra Front now staring at each other across Israel's border with Syria, the last thing the Islamists need at this pivotal phase of their jihad is a full-frontal attack from the IDF.

That would not only wipe out thousands of their footsoldiers in an instant, but would also help the Assad regime. And it would bring to the fore what even the most entrenched supporters of the Syrian uprising are now coming to realise: that the jihadists are a bigger threat to Israel's existence than the Assad regime ever was.

Meanwhile, the Islamists shrewdly operate according to the maxim, "keep your friends close and your enemies closer". As a rebel leader told a correspondent from Haaretz last year: "We will treat non-Muslims kindly, but we have a big fight against the Jews ahead. We will take that up, God willing."

Having already cruelly reneged on the promise to treat non-Muslims kindly, the apparent indifference to Mr Sotloff's religion should not distract us from a starker reality. Namely, that if the Islamic State is not stopped in its tracks, it is indeed only a matter of time before it turns its attention to the ultimate goal: the "liberation" of Jerusalem.