“The behavior of fellowship supports the claim of fellowship.”
1 John 2:6
He that saith he abideth in him ought himself also so to walk, even as he walked.
The little Book of First John is about fellowship, that is a Christian’s cooperation and participation with God in his life. John points out that if someone “says that he abides in Christ,” i.e., is in fellowship with Christ, then that person should be living (“to walk”) like Christ.
Just as fruit shows that the branch is connected to the vine, our living backs up the claim that we are in fellowship with Christ.