Gilad Shalit: A 1,000-to-one asymmetry
Behind the human drama of the Israeli-Palestinian prisoner exchange lies an extraordinary asymmetry - the rate of exchange which decrees that a single Israeli soldier equates to 1,027 Palestinian prisoners. How does it come about?
Israel's readiness to do a deal on these terms is both a strength and a weakness.
It's a strength because it reassures the country's conscript troops and their families that everything possible will be done to secure their return if they're captured. "No soldier left behind" is not just an empty phrase.
It's a weakness because it advertises to any future potential hostage-takers the high price which can be extracted from Israel for any captured soldier - perhaps for any captive citizen.
There are a number of factors behind it.
First perhaps - is the nature of Israel's army - the IDF (Israeli Defence Forces).
However Israel's critics may try to characterise it, the IDF is seen by many Israelis as a fundamental expression of their country, as well as its guardian.
National service, always badly-paid and often tedious or hazardous, is compulsory and is one of the great bonding experiences of Jewish society in Israel.
For the Jewish community - about three-quarters of Israel's population - the army is seen simply as the nation in uniform. As a result, it still produces a kind of emotional reaction which has been largely forgotten in countries like the UK or the US, which have salaried professional armies.
As President Shimon Peres said, without the Israeli Defence Forces there would be no Israel.
That creates a political pressure when a soldier is captured, which exists hardly anywhere else.
Gilad Shalit's family have turned themselves into a formidable lobbying organisation within Israel - a highly-visible presence in the national life.
Compare Sgt Shalit's fate in that respect with that of Bowe Bergdahl - the young American soldier captured by militants in Afghanistan about two-and-a-half years ago.
The American military may be making efforts to recover him, but his fate is most certainly not a daily issue in American political life.
Beyond that, there is the philosophical basis of Israel as a Jewish state.
The traditions of Judaism place a powerful emphasis on the sacredness of life and the duty to redeem or rescue captives. The Talmud (the key text of Jewish law and ethics) says that one who saves a life should be considered as though he had saved an entire world.
Prime Minister Benjamin Netanyahu alluded to that teaching as he explained to the Israeli nation why he had decided to sanction the deal to recover Gilad Shalit.
There are of course less exalted factors at play here too.
First - it's clear from history that if Israel had a credible military option to rescue Gilad Shalit it would have taken it. No military option existed to free him.
Second - Israel's enemies in these circumstances know the type of price it is prepared to pay to free its own. That knowledge helps to set a benchmark figure.
It was known or rumoured for years that Israeli governments were prepared to pay staggering sums for information leading to the recovery of Ron Arad - a flying officer shot down over Lebanon in the 1980s who is believed to have ended up for a time in the hands of the Iranian government.
It's now thought likely that he died in captivity but while there was any chance of recovering him alive, Israel was prepared to pay heavily to save him.
There's a more direct precedent too - in 1985 Israel released 1,150 prisoners in exchange for the return of three captured IDF soldiers.
The deal was more controversial at the time than the Gilad Shalit deal has so far proved for Prime Minister Benjamin Netanyahu, but it does suggest that the Israeli government of the time was making the same kind of political and emotional calculation.
Mr Netanyahu presumably calculates that the relative quiet on the West Bank and in Gaza makes such a swap more palatable to Israeli public opinion.
Egypt is a major factor too in this deal. It has ambitions to be a major power-broker in the Middle East and it has influence over Hamas, because that organisation might be looking for a new home in Cairo if the slow-motion collapse of Syria forces it to move from Damascus.
It also makes sense for Israel to sign up to a deal brokered by Cairo at a moment when its own desperately-important peace deal with Egypt has been feeling chillier than ever.
None of this should undermine the emotional power of what promises to be an extraordinary day.
The Shalit family, thanks in part to their own determination, will be made whole again. A captivity, which may have been unimaginably grim, will be over.
Many Palestinian families too on the West Bank and in Gaza will be celebrating their own moments of reunification.
At the heart of it all though, lies that extraordinary rate of exchange which tells us a good deal about Israel and the circumstances which surround it.