That which we have seen and heard we declare to you, that you also may have fellowship with us; and truly our fellowship is with the Father and with His Son Jesus Christ. - 1 John 1:3
Christians tend to throw around the word "fellowship" a lot, as in, "Let's have some fellowship," or "We'll be meeting in the Fellowship Hall." But what does this word really mean?
When Acts 2:42 says the early believers "continued steadfastly in the apostles' doctrine and fellowship" (emphasis added), it uses the Greek word koinonia, which could be translated, "fellowship," "partnership," or "communion." It also can mean "to be generous." So fellowship encompasses all of these ideas; it is far more than socializing.
Anyone can socialize. Anyone can get together and rally around their passions, whatever it is they might have an interest in. But the fellowship that the Bible speaks of is not that kind of gathering or social interaction. It is different altogether. It is people getting together to talk about the things of God.
Fellowship is praying together. It is serving together. It is giving together. It is aging together. These are the fibers of fellowship. And fellowship with God and with His people go together. As we get to know God through His Word, we will long for fellowship with other believers. The stronger your vertical fellowship, the stronger your horizontal fellowship will be. As 1 John 1:3 says, "That which we have seen and heard we declare to you, that you also may have fellowship with us; and truly our fellowship is with the Father and with His Son Jesus Christ." If you find yourself out of fellowship with God, then you will soon find yourself out of fellowship with other believers.
So if you want to be like one of the early believers in the first-century church, then you need to not only love God and study His Word, but you also need to spend time with His people in fellowship.