Have salt in yourselves and be at peace with one another.
“Everyone will be salted with fire. Salt is good, but if salt becomes insipid, with what will you restore its flavor? Keep salt in yourselves and you will have peace with one another.” Mark 9:49-50
This is in the context of holiness and purification from sin. Everyone must be purified. None is righteous in themselves. For those who have been purified and made holy, it is a tragedy for them to be defiled. Jesus is commanding us to stay pure and to be at peace with one another within His family.
We will be know by our fruit. Are we peaceable? Are we living holy and pure lives? These are evidences of genuine followers of Christ. This is what He commands.