Diotrephes slandered John, cold-shouldered the missionaries and excommunicated the loyal believers—all because he loved himself and wanted to have the pre-eminence. As typical of narcissism, personal vanity still lies at the root of most dissensions in every local church today.
The best way to combat it is to realise that discipleship means:- to deny yourself, take up your cross (death to self) & to follow Jesus.