The warning that the Torah gives over Israel

But both these views miss the point. Even though ecology and environment are important Jewish values, these values are independent of the commandment of the sabbatical year. Nor do the sabbatical year's laws prohibit eating; we may eat as much seventh-year fruit as we like if we enter the fields and pick it ourselves. The essence of the seventh year is different: it is that our servants, our guests and our beggars - Jewish or Arab or even African asylum-seekers - may eat the produce too, because their rights are equal to ours.

For the key feature of the seventh year is a restraint on ownership. The word shmittah is derived from the verb shamat, which means to "let loose" or "release". We annul debts and waive our rights of ownership over the land and its produce. We lose the right to fence off our orchards from strangers and beggars; we may neither buy, nor sell, nor trade seventh-year food; we're forbidden to store it up in a warehouse - unless we open the warehouse to the public - and we're forbidden to work on the land.

In fact, according to a minority view attributed to the school of Shammai, who taught 2,000 years ago, we can't even acknowledge an owner's rights by asking permission to enter. If we wish to eat, we must enter his land and pick our food without permission. The Jerusalem Talmud records that Rabbi Tarfon, a first-century sage famous for following the school of Shammai, was beaten up by a night watchman while eating figs without permission in the seventh year.

Waiving ownership rights over the Land once in every seven years - like the forgiveness of debts - may seem surprising in today's possession-centred societies. But even more surprising is the warning, brought in the second of this Shabbat's twin Torah readings, that failure to keep the command of the seventh year, failure to "let loose" our ownership of the Land, will eventually lead to exile.

In this second part of the Torah reading is a dramatic, poetic coda - beginning in blessings and ending in curses - that promises the Jewish people peace, security and prosperity if we keep the Torah's commandments, and dispersion into exile if we fail.

Rather than associating these curses with the Torah's commandments in general, the text connects them particularly to the commandment of the seventh year; failure to observe the sabbatical year appears to trigger exile, so that the Land may lie undisturbed, keeping its "unkept Sabbaths" that were desecrated while we lived there. Rashi, the medieval commentator, writes that "Israel was exiled for the sin of not keeping shmittah". His words echo those of the Mishnah (Avot 5:12), written shortly after the Romans destroyed our last independent Jewish state, "Exile comes because of idolatry, promiscuity, bloodshed and shmittah."

Read in this way, the biblical and the rabbinic traditions are paradoxical: they suggest that holding the Land too tightly - failing to renounce ownership in the seventh year - leads to its loss entirely. They remind us that the Land is given conditionally and temporarily, to those who merit it through their actions, not absolutely. As expressed so eloquently at the end of Behar (Leviticus 25:23), "I own the land - you are strangers and sojourners with Me."

Lord Acton, a 19th-century parliamentarian, observed that "power tends to corrupt and absolute power corrupts absolutely". Absolute ownership too, in the case of the Land of Israel, would seem to be self-destructive.

In recent debates about the future of the Land, the proponents of Greater Israel have tended to be supported by the religiously observant, while those who argued for compromise and peace have tended to be secular. Perhaps, reading the twin Torah portions ordained for this Shabbat, those who consider themselves to be observant might consider a different ideological identification.

For the authentic tradition - as expressed in the laws of the sabbatical year - reminds us that those who dwell in the Land do so as sojourners and strangers, not as owners.