The history of moral progress is rather erratic. 'An eye for an eye and a tooth for a tooth', and 'You shall love your neighbour, and hate your enemy', Jesus reminds his disciples - two moral principles once quite revolutionary. He summons his disciples to even more challenging acts of moral imagination: to abandon retaliation and to love their enemies.
These principles were revolutionary in their day. Jesus is quoting what modern scholars label the Holiness Code, in Leviticus, commonly dated to the sixth century BC. Many of its moral injunctions, particularly about sexuality, are horrifying. On the other hand, perspectives open up which are not without significance in the moral domain today. Whatever the date of composition, Leviticus pictures very graphically a primitive tribal society in which, for one thing, wreaking vengeance on neighbours who injure you was normal practice, even an obligation in honour.
'Anyone who kills a human being shall be put to death. Anyone who kills an animal shall make restitution for it, life for life. Anyone who maims another shall suffer the same injury in return: fracture for fracture, eye for eye, tooth for tooth: the injury inflicted is the injury to be suffered' (Leviticus 24: 17-20).
Surely our natural reaction is to say - fair enough? If you kill my son and heir, for example, then I may kill yours, - that's all! What would be the alternative? With mafia boss excess, I would hunt down and massacre your whole family? Here, rather, are seeds of the principle of fair compensation, the first signs of respecting the arbitration of public justice rather than condoning the fury of arbitrary reprisals. It's an advance towards civil society. The lex talionis regulates the punishment that I may expect to mete out to those who have injured me. (Leviticus even includes detailed tables of compensation.)
This moderation in regard to compensation for injuries comes, as it happens, in a speech to Moses by God (Lev 24: 13-23), preparing the people to stone to death a man who has blasphemed the Holy Name in a curse - one of the many items in the Holiness Code that we are unlikely to celebrate.
As regards the principle of loving neighbours the text goes as follows: 'You shall not take vengeance or bear a grudge against any of your people, but you shall love your neighbour as yourself: I am the Lord' (Lev 19: 18).
In fact the divine command here does not stop with one's own kith and kin: 'When an alien resides with you in your land, you shall not oppress him' - on the contrary, 'you shall love the alien as yourself, for you were aliens in the land of Egypt: I am the Lord your God' (Lev 19:34). But aliens are one thing; there is no mention of loving your enemies.
It's a beautiful chapter. The injunctions that God gives to Moses include leaving part of the crops in the fields and grapes in the vineyards in order to provide food for the poor and the aliens; being fair in all dealings with neighbours and employees; acting justly towards family and neighbours; showing deference to the aged; practising honesty in all business transactions, and much else. Loving others, clearly, means treating them justly, in a myriad of everyday ways. Nowhere, however, is there any mention of being just to one's enemies. (The Dead Sea Scrolls Manual of Discipline calls for hatred of one's enemies.)
What Jesus proposes, then, is that, rather than require compensation, you might overwhelm the wrongdoer by incredible generosity; and secondly, you might treat your enemies with the same justice as your neighbours.
In the world that we live in, as the media bear witness every day, retaliation is often wildly disproportionate. Family homes are demolished, whole villages punished, for one individual's transgression. Men murder their children to get even with their estranged wives. As for loving one's neighbours, if it includes generosity to the needy, deference to the elderly, honesty in business transactions, and suchlike, aren't we so far short of the principles in the Leviticus Holiness Code that we are simply not yet ready to hear the Sermon on the Mount?