Sects were an organization of many disparate factions that joined forces under a common cause. Sometimes, it consisted of several families. Other times, it was a bunch of people who were totally unrelated. Whatever the case may be, there was no denying that sects were the most powerful underlying force on the Xaio Continent. Even the Xia Dynasty was ruled by a sect.
There were many reasons cultivators joined sects--thee most obvious being cultivation. The primary focus of any disciple was to cultivate their inner strength, known as chi. This was done through various methods, including meditation, breath control, and specialized techniques unique to their sect. The ultimate goal was and always would be to increase their cultivation and advance through the various realms of power.