One of the first mentions of “fellowship” in scripture is in regards to the early Christians, a use that is repeated in Paul’s letters:
And they devoted themselves to the apostles’ teaching and the fellowship, to the breaking of bread and the prayers. [Acts 2:42]
And when James and Cephas and John, who seemed to be pillars, perceived the grace that was given to me, they gave the right hand of fellowship to Barnabas and me, that we should go to the Gentiles and they to the circumcised. [Galatians 2:9]
God is faithful, by whom you were called into the fellowship [κοινωνίαν] of his Son, Jesus Christ our Lord. [1 Corinthians 1:9]
The grace of the Lord Jesus Christ and the love of God and the fellowship [κοινωνία] of the Holy Spirit be with you all. [2 Corinthians 13:14]
The life was made manifest, and we have seen it, and testify to it and proclaim to you the eternal life, which was with the Father and was made manifest to us—that which we have seen and heard we proclaim also to you, so that you too may have fellowship [κοινωνίαν] with us; and indeed our fellowship is with the Father and with his Son Jesus Christ. [1 John 1:2-3]
If we say we have fellowship [κοινωνίαν] with him while we walk in darkness, we lie and do not practice the truth. But if we walk in the light, as he is in the light, we have fellowship [κοινωνίαν] with one another, and the blood of Jesus his Son cleanses us from all sin.[1 John 1:6-7]
Is it possible, therefore, for believers and unbelievers to have “fellowship”? Quite the contrary, and no where does scripture make such a possible connection. Believers and unbelievers cannot have fellowship because the unbeliever does not have fellowship with the Trinitarian God. While it is proper for us to love our enemies and pray for those who persecute us (Mt 5:44), as well as to assist our enemy in times of need so that we “heap burning coals on his head” (Pr 25:21-22; Ro 12:20), and we should of course witness to those who are lost…we cannot have the same relationship with unbelievers that we have with believers. My spending time with coworkers after my shift ends is not the same thing as having a meal with a family from my church – that’s just the reality. We call the bonding between believers “fellowship” because, like the origins of the Greek word suggests, we are “sharers” in faith and belief, united by a common God. This kind of experience cannot happen outside of companionship with believers – in fact, there are times when it can be downright dangerous, hence Jude’s warning to “show mercy with fear, hating even the garment stained by the flesh” (Jude 1:23).
When we try to decide how scripture defines a certain word, we must strive to avoid our own personal definitions, or definitions that have been given to us from anywhere other than scripture. We must permit scripture to speak for itself, and not strive to speak for it. God bless.