An extremely loaded question. Most simply, it gives us an outlet for our emotions. In more complexity, it can inspire us to make certain choices or do certain things in our lives. For example, anti-US-Vietnamese war songs in the late 1900s played a very important part in inspiring people to voice their opinions against the war, eventually forcing the US government to back out. Many songs nowadays also have such effects on us. Consider Meghan Trainor's songs against body shaming, Imagine Dragon's lyrics about following your dreams, or Linkin Park's music about not letting anyone put you down.
