1) it gives people something in common - a common national team to root for
2) participating in sports makes people healthier, and a healthier population can have less social problems and higher life satisfaction
3) it can raise awareness of the diversity in the country - by knowing sportspeople from other backgrounds (for example with migration background), people will become more aware of their countrymen
4) it can unite people in one goal, for example that of hosting a sports event. This is for example the case in soccer world cups.