Is a local congregation obligated to accept into their fellowship every Christian who seeks to be identified with them? If the answer is "yes," they are at the mercy of every hothead and trouble maker in the brotherhood. Not everyone who merely claims to be a faithful child of God is worthy of having fellowship with.
Shortly after his conversion, the apostle Paul "tried to join the disciples" at Jerusalem (Acts 9:26). The brethren at Jerusalem refused to accept this former blasphemer into their fellowship until Barnabas came and testified of Paul's character (Acts 9:27). After receiving the report from Barnabas, Paul "was with them at Jerusalem, coming in and going out" (Acts 9:28). If a congregation could refuse to extend fellowship to Paul, who among us should be exempt from having brethren check on our character before receiving us into their fellowship?
The apostle John spoke of an egotistical brother named Diotrephes. John told Gaius, "I wrote to the church, but Diotrephes, who loves to have the preeminence among them, does not receive us. Therefore, if I come, I will call to mind his deeds which he does, prating against us with malicious words. And not content with that, he himself does not receive the brethren, and forbids those who wish to, putting them out of the church." (3 John 9,10). Diotrephes was a malicious gossip who not only wanted to run the church, but ran off faithful brethren as well.
Suppose Diotrephes moved to your town and wanted to be a member of the congregation where you attend. I am sure he would tell you a convincing story of his dedication to the Lord and stand for the truth. However, any congregation who would accept him would be begging for trouble. "Can a man take fire in his bosom, and his clothes not be burned?" (Proverbs 6:27).
Several years ago a young couple asked to be identified with the congregation where I preached. The church accepted the couple on the basis of their words. We soon learned a lesson the hard way. The couple proceeded to alienate long-time friends and sow discord among brethren. I called the preacher at the congregation they had worshipped with and simply asked if they left that group on friendly terms (something I should have done before). I found out they had been responsible for splitting that congregation and causing dissension and still another group. The damage was done and there was no easy solution to our difficulty. Had we known the true character of these people, we would never had accepted them.
Though Diotrephes has been dead for nearly two thousand years, he has many descendants. If modern day kinsmen of Diotrephes are refused fellowship by a local congregation, they could still worship "in their house" (Romans 16:5). Local congregations have enough trouble the way it is. They certainly do not need to import factious brethren and gossips. "Reject a divisive man after the first and second admonition, knowing that such a person is warped and sinning, being self-condemned" (Titus 3:10,11).