Being a Christian does not mean one is believed to be a Christian.
The most important thing is that one knows he is a Christian, and the second is that others know that. One may know he is a Christian because of Romans 10:9-10, but the world knows it by whether Christians love one another.
Christ did not give the world the right to determine whether someone is a Christian. He did give them the right to judge that someone who does not love the body of Christ is not a Christian.
There is no reason for the world to believe in the love of Christ for them when the recipients of Christ’s love are unloving toward each other.
“By this all men will know that you are My disciples, if you have love for one another” John 13:35.