Why is Israel calling for UNRWA's closure, if it hurts Palestinians?

Israeli Prime Minister Benjamin Netanyahu is calling for the closure of UNRWA, the only refugee agency for Palestinians. Israel has for long criticised the UN agency saying that it perpetuates the Palestinian refugee problem. Netanyahu says while millions of other refugees around the world were cared for by the office of the UN High Commissioner for Refugees (UNHCR), the Palestinians have their own body which also treats "great-grandchildren of refugees - who aren't refugees". What is the UNRWA and what would its closure mean or a funding cut mean?