How we think about and relate to strangers is one of the keys to an ethical viewpoint. It was for this reason that the Jewish scriptures laid down rules for hospitality – leaving your fields to be gleaned by outsiders, being kind to aliens because you were once an alien in a strange land, showing hospitality (the sin of Sodom was partly the sin of inhospitality to God’s angels or messengers), or the New Testament letter to those same Hebrews puts it “do not neglect to show hospitality, for some have entertained angels unawares”.

This summer I have quite deliberately being focusing on the Holocaust and the behaviour of all those bound up in this terrible event. How can a nation that gave us Kant, one of the greatest ethical theorists, and one who believed in non-negotiable absolutes, create out of its culture and thought processes a system of belief – Nazism – which gave us one of the great embodiments of absolute evil, the work camps and death camps of Auschwitz and many other less well-known places? Ethics after the Holocaust was never, and could never be, the same again.

Primo Levi’s great books are a good place to begin this reflection. Primo Levi was an Italian Jew who formed a partisan group to oppose fascism, and was betrayed. He found himself with 150 other Italians on a train to Auschwitz. Just three of those returned home: Primo Levi because, as a chemist, he was useful to the Nazis and somehow escaped the selections so chillingly described in his book If this is a Man.

Primo Levi’s books are direct, poignant, dispassionate and heroically devoid of hate. He meditates long and hard on the nature of evil, and because the evil can never be allowed to be victorious, his books are full of detailed descriptions of characters, both good and bad, of the heroes Charles and Alberto, the pragmatists Cesar and the Greek, those who give up, those who are alone, the pragmatists who then act out of character and so place question marks over our judgements. The open-hearted generosity of the Russian peasant after liberation, the cattle truckloads of Ukrainian women, Nazi collaborators, returning home at the end of the war, the German POW crawling on all fours to receive a piece of bread from a man whose thirty relatives were murdered – these and numerous other incidents cannot fail to move you and cause you to question.

Particularly, to question our attitude to strangers, to asylum seekers, to murderers like Raol Moat or Jon Venables, to people who speak other languages or inhabit worlds alien to ourselves, to those who seem dangerous or in some sense sub-human, to those we are urgent to condemn.

The Holocaust began in small way with a re-classification, a yellow star on the coat. It escalated through burnings and evictions to the ghettos and then the transportations. At each step another layer of people’s identity, integrity and humanity was stripped away, taken by force, violated in a way which Kant could never have foreseen and which went against every tenet of Kantian ethics.

And yet this horror beyond words had its root somewhere, in culture, in ideas, in history, in religion. The signs of its fermentation were there, visibly, as Nazism took its hold on the German people. The barrier was crossed when the friend was redefined as the stranger and the stranger was cast as the enemy and the unclean – the one who must be purged for the rest of us to flourish.

This aberration turns morality on its head, for it is, as many ancient thought systems, not least Judaism, make clear, my attitude to the stranger which defines and clarifies who I am, and whether Auschwitz can happen again.