This weekend the Jewish community enjoys a double celebration: Shabbat as usual, followed immediately by the pilgrim festival of Shavuot. Shavuot celebrates the giving of the Torah to the Jewish people on Mount Sinai with a long night of learning known in Hebrew as 'Tikkun Leil Shabbat'.

I have been invited to be scholar in residence at an Orthodox synagogue in Greater Manchester. The rabbi and his wife both come from Israel. In 1983-4 the rabbi's father-in-law taught me at religious seminary in Jerusalem. It is not an exaggeration to say that most of what I know about my own religion stems from those two years spent on intensive sabbatical study with my family in Israel.

But living in Haifa much more recently also taught me what it is like for Jews, Christians, Muslims, Bahais, Druze and others dealing with everyday life in Israel.

I have come across many would-be converts in my life. There are the Jews who want to be Buddhists. Many of these 'Jubus' wander off to Dharamsala in India only to be informed by the Dalai Lama that they already have their own land and religion and should make Aliyah to Israel instead. The Dalai Lama is adamant about not converting Jews to Buddhism. Then we have the few Jews who still wish to convert from Judaism to Christianity. Paul was the first of these.

Then we have Muslims converting to Christianity. Many of these convert because of the warm meals they are offered by church people as refugees in our large cities. And lastly you have the increasing number of Christians wishing to convert to Judaism. Some are east Europeans who feel uncomfortable with the way their own churches are going back home, and think we Jews are warm and friendly. But there are cases where once converted, some of these become 'more Catholic than the pope' and then end up reverting to Catholicism after all. For these Judaism may be OK – it's the Jews themselves who are the problem.

And then we have biblical Ruth – the prototype convert to Judaism who becomes the ancestress of the Messiah. It's her story we tell on this festival of Shavuot. Ruth refuses to be put off by her mother-in-law, Naomi. She stubbornly, yet quietly, insists that going back to her own land of Moab after the death of her Jewish husband isn't an option. She wants to be with Naomi, her role model person. Wherever Naomi goes, Ruth will go. Naomi's people, the Jewish people, will be her people. Naomi's teaching, the Torah will be her Torah.

It wasn't that Ruth is needy. Rather the clue is in her name. Ruth's conversion isn't subversive like so many current conversions to Islam and Christianity. The name Ruth is an anagram for Torah, Jewish teaching. The letters of Ruth's name add up to 606, just seven short of the 613 commandments. But Ruth already encapsulates the seven Noachide laws given to gentiles.

Ruth doesn't need to convert to prove a point. Everything about her tells us she is already there.

But conversion is not a one-way process. It also implies change in the welcoming family or community. We who were (and often still are) strangers in a strange land have to love the stranger, even when she is already one of us. Conversion is the first step. In reality, we have to go on nurturing her for ever and ever.

When I was young and studying French and German for 'A' level, two books stood out. L'Etranger by Albert Camus is about a white Frenchman living in Algeria, whose mother dies and who doesn't know how to mourn. He is therefore regarded as sinful and criminal and treated accordingly by all and sundry. He is a double stranger to his community – white and French and away from home in a part of North Africa which will later explode with all the problems now faced by present-day France.

The other book is the opposite – Max Frisch's Biedermann und die Brandstifter ('The Arsonists'). This play is a satire on the takeover of Prague by the Communists, but is also a metaphor about how Hitler and his colleagues set about destroying Germany. Hitler promised the earth and delivered hell on earth.

The play depicts how ordinary nice everyday people who want to welcome strangers into their home can so easily be taken in by evil. They end up being burned alive by the guests who turn out to be entryists.

Conversion in Judaism tries hard to avoid both pitfalls. Conversion implies a gradual and incremental two-way relationship between the Jewish people and the 'outsider' who feels themselves ready and willing to take on this yoke. A convert should not be rejected, but neither should she be unduly encouraged where commitment is missing.

I was privileged in Israel to meet a genuine convert. She was from Vancouver, Canada and taught Religious Education in a school where I taught music. We came together to organise assemblies which would cater for Muslims as well as Christians and Jews. We agreed that the Book of Ruth was 'safe' for all religions and also agreed on the hymns.

Then she asked me to be a witness at the Bet Din as she wanted to convert to Judaism and needed two witnesses. I tried to dissuade her from taking this difficult step. I told her that Christianity wasn't so bad – and Judaism was difficult. It meant joining areviled people and a misunderstood land, not simply believing in one G-d. I tried every which way to dissuade her. I reminded her of all Christianity's good and positive points, but in vain.

So, finally I told her that I couldn't be a witness, as women were disbarred from this in Jewish Law – so in addition to everything else, Judaism could be considered as 'sexist', I said.

But I was wrong. The Bet Din did accept my endorsement of my friend and she was duly converted. No doubt they had been impressed by her integrity and by my own determination to dissuade her in vain.

And then the Canadian woman asked if she could lodge with me. And only today do I realise that she possibly looked on me as a role model whom she could emulate.

But now that I have been invited this weekend to tell these and many similar stories at an Orthodox synagogue in Greater Manchester, I am grateful for the opportunity of reiterating the most beautiful verses in the Bible: 'Do not urge me to leave you, to turn back and not follow you. For wherever you go, I will go. Wherever you lodge I will lodge. Your people are my people. And your G-d is my G-d. Where you die, I will die and there I will be buried...' (Ruth 1:16-17).

Yes, incremental conversion – step by step is the way – and any religion based on subversive shock tactics usually dies out in the end.

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