Circumcision of the baby boy at 8 days, known as brit milah in Hebrew, is the single most important marker of Judaism, surpassing everything else, including Shabbat.

Barring illness, circumcision of the baby boy is carried out by specially-qualified practitioners, known as mohelim, when the male baby is eight days old.

Why the 8^th day? Just think of an octave in music. Either sing, or if you possess a keyboard instrument, play the 7-note scale from doh until ti – you will realise at once that something is missing – this is the completion of G-d's covenant with the Jewish people, and it is something that the Jewish people must do themselves in order to keep their part of the covenant – and the ceremony must take place on the 8^th day.

A covenant is two-way. G-d has a special relationship with the Jewish people, first marked by our ancestor, Abraham Avinu, who left his pagan home in order to be able to carry out G-d's will and lead us to a life in service of G-d.

Brit milah – circumcision of the baby boy at 8 days- is the essential outer sign of this life of service to G-d.

In rabbinic commentary, the word brit is related to the verb barah – which is related to bara – G-d's creation of the world, but also the 'breaking of bread' as in a communal meal or service.

In his commentary on Genesis II, the great mediaeval Hebrew bible commentator, Abraham ibn Ezra (1089-1164), says: 'Most of the commentators have said that creation is bringing forth something from nothing.... Grammatically, however, the word bara can be spelled in two ways.. The first spelling is with aleph (at the end) and the second is spelt with the letter heh instead of the aleph. As in: 'And he did not eat bread with them' (II Samuel 12:17). The meaning of barah with a 'heh' is to cut, to set a precise limit, and the wise will understand.'

By circumcising a son on the 8^th day, Jewish people are re-enacting the creation of the world, the completion of the 7 days of creation. And the occasion is regarded as a great simcha, a time of food, joy, singing, dancing and celebration.

Circumcision marks the expression and dignity of self through acknowledging and internalising the Creator as one's King. It is the primary step that must be cultivated in order to ascend to the next level. The next level, attained through childhood, is complete trust and bonding to G-d – giving oneself over to G-d as a result of one's awareness and awe. That trust, bonding, awareness and awe is not possible without the initial first stage of circumcision on the 8^th day.

The revelation of the Divine also corresponds to speech ('G-d spoke and the world came into being'). Sanctity in speech leads to sanctity in desire, and together these two open doors to the inner psyche.

Holiness in speech and holiness in libido constitute a withdrawal of ego, thus leaving space for G-d and enabling divine revelation. The brit contains the idea of controlling desires. This means that in living a normal life one also exercises self-control.

This is what Avraham experienced when he underwent circumcision. Until that time his name was Avram.

In Genesis Chapter 17, G-d talks to Avram, who by now is aged 99: 'I am El Shaddai. Walk before me and be complete. I will set my covenant (brit) between Me and you and I will increase you most exceedingly.... As for Me, this is My covenant (brit) with you: you shall be a father of a multitude of nations. Your name shall no longer be called Avram, but your name shall be Avraham, for I have made you the father of a multitude of nations.'

After G-d announces this covenant (brit, implying that circumcision is part of this covenant), a new dimension is added to Avram's life. The letter 'heh', meaning 'opening', is added to his name, thus allowing the divine presence to enter into him.

It is no coincidence that this covenant takes place at the same time as guests appear – generally thought of as angels - and Abraham offers them the special hospitality that comes with the new awareness of the divine presence in life – enabled by being circumcised.

This is also why the Church preserves the Feast of the Circumcision of Jesus on January 1^st. Jesus was Jewish through and through, and so were his disciples, all of them Jewish and all circumcised on the 8^th day.

When Jews first lived in diaspora they took a solemn undertaking to obey the law of whichever land they happened to find themselves in. This undertaking is known in its original Aramaic as 'dina da malkhuta dina'.

This is why Jews have never caused trouble in diaspora.

Normally, it has been the other way round, with blood libels, ritual murder libels, forced conversions, forced expulsions, pogroms and mass murders, all carried out in the name of Christianity, and culminating in the Shoah which took place less than 80 years ago in the most civilized, best educated and Christianly Lutheran country in Europe.

Although it is incumbent on Jews to obey the laws of the land, this is only when these laws are not opposed to G-d's laws.

I asked former Archbishop of Canterbury, Dr Rowan Williams, Master of Magdalene College Cambridge, to comment on the recent decision of Iceland to ban traditional Jewish circumcision on the 8^th day.

Dr Williams alerted me to the recent biography of Martin Luther by Professor Lyndal Roper, Regius Professor of History at Oxford University. Professor Roper is the daughter of a Presbyterian Minister. In her book she exposes for the first time in English the way in which the viciously explicit antisemitism of Martin Luther himself has tainted Protestantism in general and the Lutheran tradition in particular:

On pages 395-6, this is what Professor Roper has to say about Martin Luther and the creation of the Lutheran Protestant religion:

'Nor was Luther's virulence [against Jews] repeating earlier clichés....Luther's views were not a medieval relic but a development of it. Even more disturbingly, it was not incidental to his theology, a lamentable prejudice to his thought; his insistence that the true Christians ... had become the chosen people and had displaced the Jews would become fundamental to Protestant identity. It was the central plank of his understanding of the Lutherans' providential role in history, and to secure it the Jews had to be pushed aside, discredited and, if necessary, eliminated.'

No wonder that Hitler and his followers took on the words of Luther with alacrity and, in carrying out the Final Solution, which was not so long ago, some Nazis were simply being good Protestants in following Luther's words to the letter.

Dr Williams' response to me yesterday was: 'It has to be recognised that circumcision is an integral aspect of Jewish identity, not a mere cultural extra. A ban on the practice in any country would amount to an expulsion of observant Jews.'

Jews do not want to disobey the laws of the European lands. But if forces arise that are inimical to the practice of Jewish law, such as the recent decision taken by Iceland to ban brit milah for Jewish boys at 8 days, then those laws must be disobeyed.

If Europe does not want to lose her Jews, who have brought blessings and prosperity, kindness and laughter, science, philosophy, music, art and literature to this continent, then Europeans must learn that since 1945 the 11^th commandment is 'Do not give Hitler a posthumous victory.'

We will never again allow ourselves to go like sheep to the slaughter. This means that we will never allow experts, whether doctors, psychiatrists, social workers, philosophers, or any other group (many of whose practitioners contributed wholeheartedly to Hitler's Holocaust) to dictate to us Jewish mothers and fathers how to bring up our children and grandchildren.

Without her Jews (who in many European countries preceded the onset of Christianity), Europe would be a very bleak place. Circumcision of boys on the 8^th day, the solemn covenant made between the Jewish people and G-d to obey His law and serve him to the best of our ability is Judaism itself.

To ban the practice would be to perpetrate a new Shoah all over again, and there is no doubt that the Jewish communities of Europe will resist any banning of this covenantal act, the key practice of our faith.

Dr Irene Lancaster is a Jewish academic, author and translator who has established university courses on Jewish history, Jewish studies and the Hebrew Bible.