3 John 1:10 KJV
Wherefore, if I come, I will remember his deeds which he doeth, prating against us with malicious words: and not content therewith, neither doth he himself receive the brethren, and forbiddeth them that would, and casteth them out of the church.
Barnes Notes gives three reasons Diotrophes would be chastened upon John’s arrival; three reasons why John wasn't going to forget this man's offense. When he came he would deal with it.
“… what had been done
· was public
· It pertained to the authority of the apostle, the duty of the church, and
· the character of the brethren who had been commended to them.”
So too good authority is never vindictive but always responsive to error.