From koinos (common, shared), koinōnia describes deep mutual sharing — of life, resources, spiritual experience, and purpose. 19 times. Richer than modern "fellowship" — it is the profound bond created when people share in something greater than themselves.
The early church's koinōnia was radical: shared possessions, shared meals, one body (Acts 2:42–47). Paul uses it for gospel partnership (Philippians 1:5), sharing in Christ's sufferings (Philippians 3:10), and the Lord's Supper (1 Corinthians 10:16). It is a gift of the Spirit, not a human achievement.
Koinōnia operates vertically (with God) and horizontally (with one another) simultaneously. 1 John 1:3 makes this explicit: our fellowship with one another flows from our fellowship with the Father and the Son. The Lord's Supper is koinōnia in both dimensions. Individualistic Christianity is a contradiction in terms — genuine faith creates community.