It is by any standards a strange, almost incomprehensible law. Here it is in the form it appears in this week’s parsha:

Remember what the Amalekites did to you along the way when you came out of Egypt. When you were weary and worn out, they met you on your journey and attacked all who were lagging behind; they had no fear of God. When the Lord your God gives you rest from all the enemies around you in the land He is giving you to possess as an inheritance, you shall blot out the name of Amalek from under the heaven. Do not forget. Deut. 25:17-19

The Israelites had two enemies in the days of Moses: the Egyptians and the Amalekites. The Egyptians enslaved the Israelites. They turned them into a forced labour colony. They oppressed them. Pharaoh commanded them to drown every male Israelite child. It was attempted genocide. Yet about them, Moses commands:

Do not despise an Egyptian, because you were strangers in his land. Deut. 23:8

The Amalekites did no more than attack the Israelites once[1], an attack that they successfully repelled (Ex. 17:13). Yet Moses commands, “Remember.” “Do not forget.” “Blot out the name.” In Exodus the Torah says that “God shall be at war with Amalek for all generations” (Ex. 17:16). Why the difference? Why did Moses tell the Israelites, in effect, to forgive the Egyptians but not the Amalekites?

The answer is to be found as a corollary of teaching in the Mishnah:

Whenever love depends on a cause and the cause passes away, then the love passes away too. But if love does not depend on a cause, then the love will never pass away. What is an example of the love which depended upon a cause? That of Amnon for Tamar. And what is an example of the love which did not depend on a cause? That of David and Jonathan. Avot 5:19

When love is conditional, it lasts as long as the condition lasts but no longer. Amnon loved - or rather lusted after - Tamar because she was forbidden to him. She was his half-sister. Once he had had his way with her, “Then Amnon hated her with intense hatred. In fact, he hated her more than he had loved her.” (II Sam. 13:15). But when love is unconditional and irrational, it never ceases. In the words of Dylan Thomas, “Though lovers be lost, love shall not, and death shall have no dominion.”

The same applies to hate. When hate is rational, based on some fear or disapproval that – justified or not – has some logic to it, then it can be reasoned with and brought to an end. But unconditional, irrational hatred cannot be reasoned with. There is nothing one can do to address it and end it. It persists.

That was the difference between the Amalekites and the Egyptians. The Egyptians’ hatred and fear of the Israelites was not irrational. Pharaoh said to his people:

‘The Israelites are becoming too numerous and strong for us. We must deal wisely with them. Otherwise, they may increase so much that - if there is war - they will join our enemies and fight against us, driving [us] from the land.’ Exodus 1:9-10

The Egyptians feared the Israelites because they were numerous. They constituted a potential threat to the native population. Historians tell us that this was not groundless. Egypt had already suffered from one invasion of outsiders, the Hyksos, an Asiatic people with Canaanite names and beliefs, who took over the Nile Delta during the Second Intermediate Period of the Egypt of the Pharaohs. Eventually the Hyksos were expelled from Egypt and all traces of their occupation were erased. But the memory persisted. It was not irrational for the Egyptians to fear that the Hebrews were another such population. They feared the Israelites because they were strong.

(Note that there is a difference between “rational” and “justified”. The Egyptians’ fear was in this case certainly unjustified. The Israelites did not want to take over Egypt. To the contrary, they would have preferred to leave. Not every rational emotion is justified. It is not irrational to feel fear of flying after the report of a major air disaster, despite the fact that statistically it is more dangerous to drive a car than to be a passenger in a plane. The point is simply that rational but unjustified emotion can, in principle, be cured through reasoning.)

Precisely the opposite was true of the Amalekites. They attacked the Israelites when they were “weary and weak”. They focused their assault on those who were “lagging behind.” Those who are weak and lagging behind pose no danger. This was irrational, groundless hate.

With rational hate it is possible to reason. Besides, there was no reason for the Egyptians to fear the Israelites anymore. They had left. They were no longer a threat. But with irrational hate it is impossible to reason. It has no cause, no logic. Therefore it may never go away. Irrational hate is as durable and persistent as irrational love. The hatred symbolised by Amalek lasts “for all generations.” All one can do is to remember and not forget, to be constantly vigilant, and to fight it whenever and wherever it appears.

There is such a thing as rational xenophobia: fear and hatred of the foreigner, the stranger, the one-not-like-us. In the hunter-gatherer stage of humanity, it was vital to distinguish between members of your tribe and those of another tribe. There was competition for food and territory. It was not an age of liberalism and tolerance. The other tribe was likely to kill you or oust you, given the chance. But within two or three generations the newcomers acculturated and integrated. They were seen as contributing to the national economy and adding richness and variety to its culture. When an emotion like fear of strangers is rational but unjustified, eventually it declines and disappears.

Antisemitism is different. It is the paradigm case of irrational hatred. In the Middle Ages Jews were accused of poisoning wells, spreading the plague, and in one of the most absurd claims ever – the Blood Libel – they were suspected of killing Christian children to use their blood to make matzot for Pesach. This was self-evidently impossible, but that did not stop people believing it.

The European Enlightenment, with its worship of science and reason, was expected to end all such hatred. Instead it gave rise to a new version of it, racial antisemitism. In the nineteenth century Jews were hated because they were rich and because they were poor; because they were capitalists and because they were communists; because they were exclusive and kept to themselves and because they infiltrated everywhere; because they were believers in an ancient, superstitious faith and because they were rootless cosmopolitans who believed nothing. Antisemitism was the supreme irrationality of the Age of Reason.

It gave rise to a new myth, The Protocols of the Elders of Zion, a literary forgery produced by members of the Czarist Russia secret police toward the end of the nineteenth century. It held that Jews had power over the whole of Europe – this at the time of the Russian pogroms of 1881 and the antisemitic May Laws of 1882, which sent some three million Jews, powerless and impoverished, into flight from Russia to the West.

The situation in which Jews found themselves at the end of what was supposed to be the century of Enlightenment and emancipation was stated eloquently by Theodor Herzl, in 1897:

We have sincerely tried everywhere to merge with the national communities in which we live, seeking only to preserve the faith of our fathers. It is not permitted us. In vain are we loyal patriots, sometimes superloyal; in vain do we make the same sacrifices of life and property as our fellow citizens; in vain do we strive to enhance the fame of our native lands in the arts and sciences, or her wealth by trade and commerce. In our native lands where we have lived for centuries we are still decried as aliens, often by men whose ancestors had not yet come at a time when Jewish sighs had long been heard in the country . . . If we were left in peace . . . But I think we shall not be left in peace.

This was deeply shocking to Herzl. No less shocking has been the return of antisemitism to parts of the world today, particularly the Middle East and even Europe, within living memory of the Holocaust. Yet the Torah intimates why. Irrational hate does not die.

Not all hostility to Jews, or to Israel as a Jewish State, is irrational, and where it is not, it can be reasoned with. But some of it is irrational. Some of it, even today, is a repeat of the myths of the past, from the Blood Libel to the Protocols. All we can do is remember and not forget, confront it and defend ourselves against it.

Amalek does not die. But neither does the Jewish people. Attacked so many times over the centuries, it still lives, giving testimony to the victory of the God of love over the myths and madness of hate.

[1] Of course, there were subsequent attacks by Amalek (including, according to tradition, in Bamidbar 21:1) but the decree to obliterate Amalek was issued after their first attack.