If Marine Le Pen pulls out the latest in a series of political shocks and becomes president of France in spring, kippot may disappear off the street. The National Front leader has vowed to ban religious symbols in public places as part of her fight against radical Islam and believes Jews should be ready to “sacrifice” their headgear as well.

It is almost an ironic reversion of medievalism. Jews used to be compelled to wear distinctive dress to mark them out; now they might be told to forsake a badge of identity they have chosen to wear.

The kippah has become the most visible religious emblem for Jewish men. But while it is an accepted part of Orthodox life to keep your head covered, it is not a commandment in the biblical sense. 

In this it differs from a sheitel, snood or scarf. The practice of married Jewish women covering their hair is derived from the Torah — from the ritual of the sotah, the test of a woman suspected by her husband of infidelity. From the instruction to the officiating priest to “uncover her hair”, the rabbis understood that a married woman should not go bare-headed.

So how did the kippah arrive on Jewish heads? The religious rationale is explained in Moshe Becker’s short, new book, The Kippah, written by an Israeli-trained American rabbi who works in New York City’s education department.

The Talmud contains a number of references to men covering their hair, notably Rabbi Huna, of whom it was said he “would not walk four cubits with a bare head. He used to say, ‘The Divine Presence is above my head’”. (Some derive the word yarmulke from the Aramaic yoreh Malka, “to fear the King”. An alternative is from the Turkish, yağmurluk, rain gear, or yarim and qap, half-hat).

From such sources you might conclude it was regarded as fitting for a man of distinction such as a rabbi to wear a hat, but not necessary for all. But from other discussions about what was required to lead prayers, Rabbi Becker determines that generally a man was expected to go about with head covered. He acknowledges, nevertheless, that there is no classical text which explicitly requires this and, according to some authorities, “one may even recite the blessings and the Shema with a bare head”.

The mystics thought otherwise. If a man walks four cubits with a bare head, warned the central kabbalistic text, the Zohar, “his life will depart from him”.

While some medieval rabbis taught that one should cover one’s hair as a sign of humility before the Divine Presence, others stopped short of making it obligatory.

Rabbi Meir of Rothenburg, Maharam, said there was “no prohibition” against walking bare-headed. Maimonides observed, “The great men among our sages would not uncover their heads because they believed that God’s glory was around them and over them.” 

By the 16th century, the Shulchan Aruch, the Code of Jewish Law, regarded its adoption as universally desirable, instructing that one should “not walk four cubits with a bare head”. It noted the opinion of those who said it was forbidden to mention God’s name with a bare head and who objected to anyone entering a synagogue with head uncovered.

But still there was not consensus. The influential 18th-century Lithuanian sage, the Vilna Gaon, for example, stated: “Only in the presence of important people and while praying, it is proper and correct [to cover one’s head]”.

Advocates of covering, meanwhile, cited a new motivation. The 17th-century rabbi, David Halevi Segal, known as the Taz, wrote: “It is an established custom among the Gentiles that as soon as they sit down, they remove their hat.” Therefore, by covering one’s head, one obeyed the religious principle of chukat hagoy, to avoid following “the practice of the Gentiles”.

Rabbi Becker notes the early Christians were instructed by Paul to doff hats when praying as a matter of honour (the contrary was thought true for women). Rabbi Moses Schreiber, the Hungarian authority known as the Chatam Sofer who lived from 1762 to 1839, wrote: “Once the Gentiles have established as a religious practice to be bareheaded and to honour their worship thus, the same becomes prohibited for us according to the letter of the law… This custom was established for them with respect to males, but not females.”

By the 19th century, the Chafetz Chaim (Rabbi Yisrael Meir Kagan), whose work Mishnah Berurah remains an authoritative guide to ritual, could recommend even covering your head when asleep.

In the 20th-century, the leading American halachist, Rabbi Moshe Feinstein ruled you could take off your kippah if required to at work but you should put it back on when you left the office. 

So deeply attached are observant Jews to their kippot they can remain intact even in the most testing circumstances. In the book’s preface, Rabbi Sender Haber, from Norfolk, Virginia, recalls the time he was withdrawing cash from a dispenser, kippah on head, when he felt himself under the gaze of a woman parked nearby. He went over to see if there was a problem. 

But he quickly found there was nothing sinister in her interest.“I’ve been watching you stand outdoors in a hurricane for five minutes,” she told him, “and not once has your little hat blown off of your head.”

The Kippah is published by Mosaica Press at £11.80