Jerusalem's busy Mea Shearim neighbourhood is witness to a looming demographic dilemma for Israel.
By Tim Franks
BBC News, Jerusalem
Haredi life is devoted to studying Jewish law and thought
It is an almost exclusively ultra-orthodox Jewish enclave, its narrow streets and crowded apartments teeming with thousands of black-hatted, white-shirted Haredi men and their families.
The Haredim live in a world apart from modern, westernised West Jerusalem, devoting their lives to the study of Jewish law and thought, practising what they see as the purest form of Judaism.
It is widely accepted that Palestinian population growth in Israel and the occupied territories is a major strategic issue for Israel.
But the proportion of ultra-orthodox Haredi Jews is also growing, approximately three times as fast as the rest of the population.
In a country where every 18-year-old Jew is supposed to join the army - and which has faced six major conflicts with its neighbours and battled two Palestinian uprisings - that Haredi population growth poses some urgent questions.
The ultra-orthodox do not face compulsory conscription; they are exempted from national service in order to continue their religious studies.
Once it was a tiny minority which took that route; now they account for more than 10% of draft-age Israeli Jews. By 2019, the government forecasts they will constitute almost one in four.
Secular Israelis see the army as the state's most important institution
Former Deputy Prime Minister Yosef Lapid represents a constituency in Israel that asks whether Haredi behaviour is not in fact undermining the Jewish state.
"I have nothing against them because they are religious," says Mr Lapid. "I very much oppose the fact that they don't serve in the army. They represent God in God's country, but don't defend God's country".
From the yeshivas, or theological colleges, around Jerusalem, where the young men sway back and forth as they read and debate centuries of law and commentary, there is a different view.
They believe that the country has spiritual as well as physical needs, and there is no greater service than that of religious study.
"The difficulty a secular Israeli is going to have is just not understanding the whole world-view that the religious world is coming from," says Haredi rabbi Moshe Zeldman.
"If you look at the whole history of the Jewish people, it can't be explained in physical terms. What made us survive this long? We really believe God has a hand in history," he says.
Rabbi Zeldman says he is not living in a dreamland, where only God takes care of the Jews and Israel does not need an army.
The Haredi issue will become more central as the population grows
"You also need a balance. And the balance has to be that as much as you're worried about your physical survival, you're also focussed on your spiritual survival," he says.
But there is a further source of tension - the economy.
At a food distribution scheme in Mea Shearim, dozens of families come to collect cardboard boxes full of all types of kosher food.
This is not an unusual sight, because most Haredim are poor and many rely heavily on welfare. Government figures suggest that two out of three Haredi men do not have a paid job.
More and more, Israelis are asking if this too can carry on.
Demographer Mencahem Friedman says that either the Haredim will have to change their ways or "the government will force them" to contribute more to the economy and defence.
"To keep the status quo as it is now probably will not be possible," he says.
"Everyone has to make a very crucial decision to change the situation. How they will make it, I don't know."
It is one of the most difficult questions of all for Israel - what a Jewish state should demand of its own Jewish citizens.