The Fellowship of the Saints

Consider Acts 2:41-42. As people repented and believed, they were baptized and added to the church. Then they continued steadfastly / devoted themselves to the Apostle's doctrine. They also continued steadfastly / devoted themselves to fellowship – only there is a definite article in the Greek text – "the fellowship." So it is not just the act of fellowshipping. It is the fellowship as a group / church. that they were committed to. – a partnership; a working relationship with the Lord and with other believers.