This is how human persons achieve their fulfillment in relationships with others, in companionship with others. That was just one of the many divisions that Jesus wanted to close. Association brings people together. By association, individuals overcome isolation. If association is denied, the path to a fuller life is foreclosed.
Phone books list all kinds of associations.
They reflect an impressively broad range of human activity. There are associations that use other labels like league, union, federation, council, or conference. Catholic social teaching has a nice link at this juncture with Catholic sacramental theology. Association relates to companionship, and companionship, in the Catholic view, relates to Eucharist. Eucharist is a bread-breaking ritual.