The lifeblood is beginning to drain from Gaza's historic but tiny Palestinian Christian community. Numbering more than 2,300 at the time of Israel's occupation of the Gaza strip in 1967, the Christian community should have grown in line with the rest of Gaza's population to around 10,000 today. Instead the figure has halved, to barely 1,200. Emigration is the driver of this precipitous decline. Christians are voting with their feet to escape 40 years of Israeli military occupation, followed by almost 10 years of an Israeli and Egyptian blockade which has left the tiny territory and its 1.8 million inhabitants on the brink of a humanitarian catastrophe.

As a result of the hardships caused by the blockade, including chronic food and water shortages, a collapsing health system, increasing infant mortality and the highest unemployment in the world, Palestinian Christians are now leaving Gaza at the rate of between 50-100 a year. I personally know some of those who have left, or who are thinking of leaving. The irony is, the exodus happens at the very time, Easter and Christmas, when the indigenous Christians of Palestine should be celebrating their connection with the land, and to the story of Jesus. After all, if one assumes that St Philip continued his angel-inspired evangelistic journey to Gaza after baptising the Ethiopian eunuch (Acts 8:26-40), then some of the earliest followers of Jesus would have been found in the small coastal territory.

Whether there are any Christians left in Gaza within a generation remains to be seen. The festive exodus is occurring because Easter and Christmas are the only times when Israel allows Gaza's Christians to leave the territory, other than for urgent medical reasons. Even then, a third of medical-related applications from Gaza are denied by Israel, according to a recent report from the United Nations.

In March this year the Washington-based news website Al-Monitor told the story of Karam Qubrosi, a 28-year old Palestinian Christian from Gaza who was given a permit by Israel to pray at the holy sites in Jerusalem for Easter. He was surprised to receive such permission, since Israel had previously only rarely allowed Palestinian men under the age of 35 to leave Gaza. But having obtained his permit, he was not going to lose his chance: he told Al-Monitor that he planned to stay outside Gaza and settle in the occupied West Bank. Another Palestinian Christian will have left.

Israel seems to have shifted its policy towards the Palestinian Christians of Gaza. This Easter a record number of 847 permits were issued to the Christian community, that is to some two-thirds of the total Christian population. Writing on the website of the Latin (Roman Catholic) Patriarchate of Jerusalem in March, the Brazilian parish priest in Gaza City, Fr Mario da Silva, said this meant that nearly all of the 890 applications to travel received through his church had been allowed.

Fr Mario praised God for His grace, but the long-term implications for his tiny flock, and that of the Greek Orthodox parish which is the other main Christian community in Gaza, are worrying. I understand from local sources that this year some 40 Palestinian Christians left Gaza for the Easter celebrations in Jerusalem with no intention of returning. The Palestinian Christian community is at risk of a slow death from a thousand cuts.

The reason for Israel's changed approach to exit permits is unclear. But in many ways the existence of a historic Palestinian Christian community in Gaza is, for Israel, an inconvenient truth. It undermines the narrative which suggests that Gaza consists of almost two million hard-line Islamists who want to sweep the Jews into the sea. It would certainly suit Israel's long-term purposes, which are to place a hermetic seal around Gaza and separate it from other parts of Palestine, if all the Christians left for Ramallah or Bethlehem in the West Bank, or further afield (anywhere but Israel itself).

Islamist extremism is the elephant in the room. The Hamas regime in Gaza has generally been tolerant towards the Christians, recognising their wider contribution to the community through education and healthcare. And it is true that the Christian community punches way above its weight in terms of its involvement in society: the Palestinian Christian witness in Gaza includes five excellent schools, a general hospital, four primary healthcare clinics, two vocational training centres, a YMCA community centre and several other social projects. The beneficiaries of these projects are nearly all Muslims.

But as the humanitarian situation in Gaza gets worse, and the United Nations has predicted that the territory will be 'unliveable' within 3-4 years, so the risk increases that more extreme Islamists gain a foothold. Hamas has so far managed to suppress any signs of the so-called Islamic State emerging in its territory, but the Christians are not taking this for granted. They only have to see what happened to their co-religionists in Iraq and Syria. Hence the need to keep all options open.

When you talk to the Palestinians Christians of Gaza, as I do on my trips to the territory, what strikes you is how proud they are of their Palestinian identity. And they feel deeply for their fellow Gazans, 99.9 per cent of whom are Muslims, who do not receive such apparent munificence at the hands of the Israeli permit regime. For these Palestinians, driven to despair by their desperate situation, there seems no way out. No wonder the suicide rate in Gaza is on the increase.

The Palestinian Christian witness in Gaza offers hope in the face of such desperation. Embrace the Middle East is the biggest UK funder of such projects. We support this historic witness not because we want to preserve some quaint Biblical museum piece, but because the Christian hospital, clinics, training centres and schools are a vibrant expression of faith and provide vital services in a community which is suffering grievously. A community which has been devastated by regular wars and by the privations caused by a blockade which next year sees its 10th anniversary (alongside the 50th anniversary of Israel's occupation). The Palestinian Christians of Gaza are the quintessential 'salt and light' in the very land where Our Saviour called us to be such. It would be a tragedy if that powerful witness were to come to an end.

Jeremy Moodey is chief executive of the Christian development charity Embrace the Middle East, which supports the social witness of the historic Christian communities of the region. Embrace has launched a summer appeal highlighting the work of the Palestinian Christians in Gaza.