There's a long answer to that. I'll try to keep it tight. The United Nations is not a monolithic body. It has six principle organs. The United Nations has the Security Council, where Israel has enjoyed a privileged position by virtue of its special relationship with a permanent member there. The Israelis have no problem with the Security Council, save and except for decisions that have been taken by the Security Council that they have violated for many a year.
Second, with respect to the General Assembly, Israel has a real problem there, and it's because the political dynamic of the General Assembly is different. It's top-heavy for the global south, which has historically been very supportive of the Palestinian people by virtue of the historical ravages of colonialism and imperialism and so on, so it has a problem with what the General Assembly says.
It also has a problem with the Secretary-General. They have indicated to him that he's a persona non grata. That would deal with the UN Secretariat. That's another body of the UN. When the International Court of Justice was looking at this last advisory opinion, the Israelis called this a form of legal terrorism, and so on.
The problem has to do exactly with what Professor Antonius said. The United Nations is a standard-bearer of international law, and when the UN bodies pronounce upon Israeli actions in the occupied Palestinian territory and determine those actions to be unlawful, understandably, the Israelis don't like it. This is the basis of their concern with the UN.