How are evangelism and fellowship related?
In Matthew 28:19-20, we see Jesus give his disciples the great commission to make disciples, and in Acts 1:8 he says that they will be his witnesses to the world. In the book of Acts we see this lived out in two ways. First, we see the preaching of the gospel in public, and we see people responding to the preaching of the gospel. Second, we see people living out their faith authentically, and that the surrounding community responds to this authentic love for each other by wanting to be part of it. This is most clearly expressed in Acts 2:42-47, where the church is said to live out their faith, and God adds to their numbers daily. I think this was a real life example of Jesus' words in John 13:34-35,
34 "A new commandment I give to you, that you love one another, even as I have loved you, that you also love one another. 35 "By this all men will know that you are My disciples, if you have love for one another."
How though are people, not in the church, to see this love for one another if we only do it while we are with other Christians? Well, there seems to be two ways this can happen. First, the great commission is probably more accurately rendered, “while going, make disciples,” which indicates that Christians are still supposed to be out and about in the world. Therefore, while we are going about in the world we can show other people love, but we can particularly show people how Christians interact well with each other. We should treat each other with respect, fairness, kindness, love, etc. in front of other people. On the other hand, if we are regularly bad mouthing other Christians to our co-workers, neighbors, non-Christian friends and family, etc., then we are doing exactly the opposite of showing people Christ's love, and we may well be leading away from the Lord.
A second way people can see our love for each other is by inviting them to join in our fellowship. In the very early church, they often met in the temple courts and therefore, their behavior was open for everyone to see. Following that, Acts describes many times when the Apostles seemed to have large meetings open to many types of people. The love and acceptance in a health church body can be very appealing to a someone who has not experienced that sort of thing, and from my experience can often break down barriers of unbelief in people who are deciding for the Lord.
We need to have regular times where we as a body are inviting people into our fellowship so that they can see how God really changes people. This does not mean that we need to be perfect, but rather that we can love each other in spite of our obvious flaws, just like God does for each one of us. This practical show of unconditional love can help people believe in a God who gives unconditional love.
Evangelism divorced from the fellowship of the body of Christ is not really telling the whole gospel. The gospel is not simply the good news about eternity, but rather it is the good news of salvation which includes the Holy Spirit's transformation of us right now. The place that God planned to highlight that transformation is in and through Christians living and loving each other. Therefore, our fellowship and community is not just for our sakes, but a tool that God wants to use to bring more people to Himself. Likewise, the most effective outreach to the world should include presenting the image of a healthy loving church.
PS. As a final thought, I believe that one of the reasons the church as a whole in America has not been effective in reaching more people is because we do not love each other well, and thus do not present a very appealing image of God's love. The better we love each other the better we will be able to attract people to God's love.