What does it mean to be part of a comminuty?

If you hold someone's hand, chances are they will hold yours in return.

First and foremost, members contribute to said community, but at the same time community members are usually there for the gain as well.  In a mindset of "One for all, all for one", it's give and take.

Basically the basis of the community is to contribute to it and profit from it.

Personal goals and community goals are usually very much the same. Everyone is striving for the same goal, for the goal of everyone else. Members are the building blocs of the community.  The more members a community gets, the more network everyone then has to profit from.  Therefore, the community is always looking for new members, for contributors.