By Jeremy Bowen
Middle East editor, BBC News
Violence moves faster than negotiation. Now that Israel has its tanks in Gaza, military force will drown out everything else until Prime Minister Ehud Olmert decides that his business there is done.
Israelis will expect a strong response from their leaders
In his office in Jerusalem, Mr Olmert is facing the most important test for any Israeli leader - how well he handles a military crisis. Those who fail the test, suffer severe political damage.
Israel hopes that the presence of the troops and armour will persuade the Palestinians holding Corporal Shalit to give him up. But what if that does not happen?
The Israelis will not turn round and go home if they do not get their man back quickly.
The army and air force will go onto the offensive, aiming perhaps to destroy what it calls the Hamas terror infrastructure.
Attempts to assassinate Hamas leaders are also possible.
Israeli attacks will be resisted, which will be highly dangerous for all concerned - especially Palestinian civilians caught in the middle.
Israeli pressure always produces a reaction on the Palestinian side.
It will strengthen the resolve of the Hamas military wing and other militant groups to fight.
The Gaza crisis puts more pressure on the Palestinian leadership
Among the politicians, it might be the catalyst for the establishment of a Palestinian government of national unity.
Before Israel moved its troops in, Fatah and Hamas, the two main Palestinian factions, sealed an agreement that the Hamas prime minister Ismail Haniya and the Fatah president Mahmoud Abbas have been working on for some time.
In it, Hamas accepted the idea of a Palestinian state on the West Bank, Gaza and east Jerusalem.
Because of what they did not say, it can be interpreted as an implicit recognition of Israel. Hamas people moved
quickly to challenge that.
One of the Hamas MPs, Salah al-Bardaweel, told the Reuters news agency that "We said we accept a state (in territory occupied) in 1967 - but we did not say we accept two states."
Had Ismail Haniya stood up on the morning after the Palestinian elections in January and said what he has agreed to now - accepting that President Abbas can negotiate for a state only on the land occupied since the 1967 war - he would have had a warm reception from some Western countries at least, and might even have headed off moves to isolate his government internationally.
There have been suggestions that Haniya is losing the internal debate within Hamas
Since there have been no peace negotiations worth talking about between Israel and the Palestinians for more than five years, and there is no immediate chance of them restarting, the discussion, for now, is theoretical.
But in the months since then, the political background has changed.
The big powers have cut off the money that the Palestinians need to run their government and to pay their soldiers, teachers and doctors, which has caused great hardship.
They have established three tests that the Hamas government must pass before the money tap is turned on again - recognising Israel, giving up violence and accepting past agreements.
The Palestinian deal falls well short of that.
The most important thing the agreement does for Palestinians is to reduce the tension between the leaders of Hamas and Fatah, the two most important factions.
Do not forget that their men have been fighting each other on the streets and that there has been talk of a Palestinian civil war.
Escalating violence could derail any peace initiatives
Palestinians feel very uncomfortable about splits, and are always conscious of the pressure and power radiating from Israel.
Their deal might end up to be worthless if the multiple pressures on the Palestinians destroy the shaky unity that Messrs Haniya and Abbas are now proclaiming.
The agreement would be worth more if both men were masters of their own houses.
But both men have been weakened, and one experienced negotiator here in Jerusalem commented that weak plus weak usually equals weak.
Abbas was weakened by the defeat of Fatah at the elections and the fact that Israel does not take him seriously; Haniya by the pressures of government, the international financial sanctions, and now the abduction of the Israeli soldier Corporal Gilad Shalit, which seems to have taken him by surprise.
There have been suggestions that Haniya is losing the internal debate within Hamas.
Some suggest that there is a strengthening of an axis between the Hamas military wing in Gaza and the exiled leadership of the movement in Damascus - and that the prime minister is the odd man out.
But in this conflict, the different sides have spent years building bigger defences around their own beliefs, and deeper ditches between each other. So, some believe that movement, however small, ought to be applauded.
The European Union thinks Hamas has moved, a little bit. It says the agreement is a good first step.
If there were Israelis and Palestinians and strong outside powers who wanted to create something bigger, it could conceivably lead somewhere.
Perhaps it is a seed for the future.
But first, this place is preparing itself for the more familiar realities of blood, bulldozers, bullets and bombs.