Fellowship is first the sharing together in a common life with other believers through relationship with God through Jesus Christ. Fellowship is first and foremost a relationship, rather than an activity. The principle is that any activity that follows should come out of the relationship. In Acts. 2:42 the early church was not merely devoting itself to activities, but to a relationship. It was this relationship that produced an active sharing in other ways. It is so important that we grasp this. Fellowship means we belong to each other in a relationship because we share together the common life and enabling grace of Jesus Christ.
"Do not be yoked together with unbelievers. For what do righteousness and wickedness have in common? Or what fellowship can light have with darkness?” 2Corinthians 6:14