The UN was set-up directly after World War II, with countries part of the Alliances. Winston Churchill (a known Freemason) co-created the UN.
The UN helped create Israël as a country. In 1948, the state of Israël was officially announced, after 55 years of Zionism, fighting for Jewish land. Since the start of Zionism at the end of the 19th century, many Jews already moved to the area later declared Israël.
Israël is a member state of the UN since 1949. In the year before (1948), they were already acknowledged by many countries. Ever since (and before), there have been problems with neighbouring countries.
The UN formally tried to protect Arab nations around Israël. Link to wikipedia page of UN-resolutions mentioning Israël. Many Jewish people feel the UN is working against them. This certainly helped in adding muslim countries and developing countries to the list of member states.
Note how most UN-resolutions were given before 1989? In politics, it is never clear who really is powerfull behind the scene in any organization. The best power plays are done behind the scene.
Who is running the United Nations, really? I want to know.