ANSWER: Meeting with others who are also converted and have the same general beliefs, also known as fellowshipping, is an essential element in our spiritual growth and development. The World English Dictionary basically defines fellowship as the act of people sharing activities, goals, interests, duties, trials, troubles and alike with one another in a group.
Strong's Exhaustive Concordance of the Bible has six different definitions for the word fellowship. Although these definitions are useful and correct, the simpler one is that fellowship is simply sharing something together with other humans.
There are two basic elements or foundations that are needed for true Christian fellowshipping to occur among believers. The first foundation is that those who meet together should have things in common like beliefs (Acts 2:42), work (Nehemiah 4:1 - 23), faith (1Samuel 20:30 - 42), need (2Corinthians 8:1 - 15) and what they struggle against (Daniel 3:16 - 30). Other areas of commonality include common purpose ('How wonderful it is, how pleasant, for God’s people to live together in harmony!' - Psalms 133:1), conviction ('you must all have the same attitude and the same feelings; love one another . . .' - 1Peter 3:8) and hope ('There is one body and one Spirit, even as you were also called in one hope of your calling;' - Ephesians 4:4).
The second foundation of fellowship is in what is shared. Believers should share in the responsibility of helping fellow Christians who lack the essentials of life (2Corinthians 8:4). They should also share in what it takes to preach the gospel to the world ('I (apostle Paul) thank my God for you every time I think of you . . . 5 because of the way in which you have helped me in the work of the gospel from the very first day until now.' - Philippians 1:3, 5, see also Galatians 2:9). What should be also shared is the power of God's spirit to bring people together ('Your life in Christ makes you strong, and his love comforts you. You have fellowship with the Spirit . . . - Philippians 2:1). Another element is that those who meet should all desire to walk in the light of God's word (1John 1:7). All believers should share in what is called the 'Gospel mystery' (And that I (the apostle Paul) might enlighten all as to what is the fellowship of the mystery that has been hidden from the ages in God . . . - Ephesians 3:9). There are several other things believers should share in but only a few are listed here to spur further study of the Bible.
Fellowship, as a noun, or as action, demonstrates who we are. It allows us to interact with others who share common beliefs and sentiments. It allows us to recognize our own faults and gives us the opportunity to share in the spiritual growth of others. Moreover, as we have seen and as the Bible confirms, this is highly pleasing in God's sight. We should practice this outstanding spiritual trait whenever we can. Thank you for your question about what is fellowship.