What is the best way to cause volcanic eruptions amongst Jews worldwide?

The answer, unfortunately, has just been found in Jerusalem.

The decision by Prime Minister-in-waiting, Benjamin Netanyahu to create a new “Jewish-identity-authority” in the Prime Minister’s Office has started to caused tremors in the diaspora.

The task of the agency will be to re-examine the fiendishly difficult question of deciding who is (and also, therefore, who is not) a Jew.

Of course, the Woody Allen school of thought will jest about definitions to do with eating gefilte fish (but forgetting how Ashkenazi-centric that is) or phoning your mother twice a day (why not more?).

But, this is a very serious issue and the stakes are high. It is not just a philosophical question, but also a very practical one. It affects the citizenship of the world’s only Jewish country. It also threatens to challenge the identity of millions of Jews outside Israel.

It is also, as many JC readers will note with a sigh, not a new question. Back in 1958, then Prime Minister David Ben Gurion consulted Jewish religious and legal experts world-wide to find a water-tight definition, and found it exceedingly difficult.

How to define us? We are not just a religion - for there are plenty of Jews who are atheist, but still strong in their Jewish identity. But nor are we a race – for non-Jews can convert to Judaism.

The Law of Return – originally passed in 1950 by the Knesset, which guarantees citizenship to anyone Jewish – has gone through many proposed and actual amendments over the years struggling to encompass both religious and secular viewpoints. It is currently anyone with at least one Jewish grandparent or has converted to Judaism.

This is still problematic, as it begs the question of whether the individual with a Jewish grandparent can belong to another faith. It also leaves open as to which religious authority supervises the conversion, as the Orthodox do not recognise those of other Jewish bodies.

The result is various anomalies, such as someone having full citizenship and fighting in the Israeli army, but being denied a wedding or burial by the Orthodox groups that control them.

But at least the compromise has more or less worked thus far. However, this may change for the worse, given the clearly stated demands of most of Netanyahu’s current political allies – the religious parties – to seize control of Jewish identity and use exclusively Orthodox criteria.

They wish to limit conversion to a Jewish mother or conversion by an Orthodox Beth Din. By putting Avi Maoz of the ultra-Orthodox Noam party in charge of this new “Jewish-identity-authority”, the great fear is that this change will be pushed through as the price for supporting Netanyahu.

What will happen to the millions of Jews around the world whom this will exclude from citizenship? Even if they have no intention of making aliyah, it will cast doubt on their Jewishness in their own eyes as well as their peers.

And is it unreasonable to assume that these people will be less inclined to support Israel from the Diaspora -support that Israel has long counted as a given.

What about those born of a Jewish father? Those who converted through Conservative, Reform or Liberal B'tei Din? Or their children and grandchildren? Or the Russian Jews with a Jewish grandparent who suffered for their Jewish identity and flocked to Israel in the 1980s? Or the Ukrainian Jews fleeing Putin’s missiles right now?

Will Israel become the one country in the world to deny Jews the right to Jewish identity?

Will it be easier to be Jewish outside Israel than inside?

Benjamin Netanyahu is keen to be Prime Minister again, but is he willing to fracture the Jewish world...and to have the terrible legacy of being labelled by some as the first anti-semitic Israeli head of state?