I think the basic purpose of national government is to protect individuals. Nations exist to protect people within their borders militarily from other nations, (Hostile nations have a tendency toward genocide).
People have a habit of getting riled up when their rights are violated, throwing revolutions and whatnot, so after life and limb governments have to protect citizens rights.
A lot of people seem to think nation's exist to promote capitalism, trade, prosperity, etc. Most everyone wants prosperity, so they think governments should try and produce it.
History has taught us that governments have more power to destroy trade then they do to promote it. It's not their role. Economies are chaotic dynamic systems we ill understand. I would rather government gave up on promoting the economy, and instead focused on not hindering it.
Now sometimes a nation will shoot itself in the foot economically, so the people have to step in and set some rules. People are dumb, they will invest in various pyramid schemes, etc. I'll go along with a small amount of government interference.
I don't mind when the government requires transparency in business dealings. If a whole nation admits some disaster is occuring within it's economy I'll support the minimal interference in said economy required to correct that specific disaster.
Anyway, given that, I believe the proper role of the UN to be a tricky concept. The UN is ruled by nations. It is a representive democracy, of a sort, if you assume nations represent their people. Some do more then others.
As a result the UN can never interefere too much in national sovereignty, or it's true masters, the rulers of nations, will rebel.
Still, if enough UN nations are actually representing the will of their citizens, then the will of the citizens in the UN get's translated, somewhat, to the UN.
I think people are most about their own rights, and those of their children, family, etc. As such I support UN resolutions that attempt to protect rights.
Even the resolution that got me most fired up was designed to protect a perceived right. I just think it trampled too much on other rights, and it was protecting a perceived right that is impossible to protect in this day and age.