Saturday is Yom Kippur, the Day of Atonement, the holiest day on the Jewish calendar. It ends a run of days beginning from the Jewish new year, which was last Thursday, in which those who have done wrong are given a last chance to set things right. According to tradition, a person's fate for the coming year is set on this day. Today is the last-chance saloon.

But there is another dimension. The famous 19th/20th century Jewish ethnographer and playwright Shlomo Ansky tells a story about Yom Kippur. This was the only day of the year when the high priest was allowed to enter the Holy of Holies at the heart of the Temple. There he would utter the name of God. And if, Ansky writes, at this critical moment, the high priest – the holiest man, in the holiest place, on the holiest day – has one impure thought, then the world will be destroyed.

The Temple, of course, was destroyed by the Romans in AD70. From then on, Judaism became a religion of books and teachers, rather than one of temples, sacrifices and priests. And though religious Jews pray daily for the restoration of the Temple, they are forbidden onto the Temple Mount in Jerusalem – politically because, since the late 7th century, it has been the site of the al-Aqsa mosque and the Dome of the Rock; theologically because, according to Jewish law, it would be wrong for any Jew to walk over the site of the Holy of Holies without the proper purity preparation and potentially thinking impure thoughts. And no one now knows where its exact location was. So Jewish access to Temple Mount has been strictly forbidden (by religious, not secular, law) for centuries – though some of the more secular Israeli nationalists increasingly want access simply to insist upon their jurisdiction over that part of Jerusalem. It was Ariel Sharon's deliberately provocative visit to the Temple Mount on 28 September 2000 that sparked the second intifada. In the five years of fighting that followed, thousands of people were killed.

The orthodox position has long been that the Temple can only be rebuilt and sacrifices resumed when the Jewish messiah returns. There have been a few dissenting voices to this consensus – most notably, Maimonides – but since the foundation of the state of Israel, the idea of Jews returning to Temple Mount prior to the arrival of the messiah has been the obsession of a tiny minority. And mostly, like Sharon, driven by secular political rather that theological concerns. But as Israel continues its shift to the right, these dangerous voices are now entering the political mainstream. Back in March, the housing and construction minister Uri Ariel, who advocates the rebuilding of the Temple, visited the site as a "tourist". In April, Knesset member Miri Regev emphasised: "I do not understand why a Jew is not allowed to pray in the most sacred place for him – the Temple Mount." Religious services minister, Naftali Bennett, has announced he will work for legislation guaranteeing Jewish access. And the notoriously hardline Likud politician, settler and Knesset member Moshe Feiglin – who believes Israel ought to annex all of the West Bank and Gaza – stepped up the pressure on Binyamin Netanyahu in a speech in New York last week, calling on him to restore Jewish sovereignty over the site.

It would be hard to overstate how dangerous an idea this is. The vast majority of orthodox rabbis have reiterated their opposition to it. But the settler mentality is now increasingly focusing on what is politically the most explosive site on the planet. If they succeed, a billion Muslims worldwide would go ballistic. Shlomo Ansky got it more or less right about the potential consequences of impure thoughts on Temple Mount.

Twitter: @giles_fraser

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