The United Nations is the preeminent institution of multilateralism. It provides a forum where sovereign states can come together to share burdens, address common problems, and seize common opportunities. The U.N. helps establish the norms that many countries - including the United States - would like everyone to live by.
Human rights, race relations, gender politics, health care, and foreign policy - it's a lot to keep track of, and yet all of these things affect us in our daily lives. Making sense of everything requires meticulous unpacking of feelings, delicate navigation of social norms, and a community of love to help along the way.
There are those who would draw a sharp line between power politics and a principled foreign policy based on values. This polarized view - you are either a realist or devoted to norms and values - may be just fine in academic debate, but it is a disaster for American foreign policy. American values are universal.