Mark 9:49-50

⁴⁹ “For everyone will be seasoned with fire, and every sacrifice will be seasoned with salt.

⁵⁰ Salt is good, but if the salt loses its flavor, how will you season it? Have salt in yourselves, and have peace with one another.”

Verse 49, taken in its context, reaches back to the unquenchable fire of Gehenna (v.48), and forward to the self-discipline of verse 50. … Every one must be salted somehow, either with the unquenchable fire of Gehenna or with the severe fire of self-discipline. Wise is he who chooses the latter alternative. … Jesus once called His disciples the salt of the earth (Matthew 5:13). He warns them now (v.50) not to lose their saltness. … [This warning may be connected with] the dispute as to who would be greatest in the Kingdom of Heaven … If the preserving principle embodied in the Apostles, and which was to emanate from them, should itself prove corrupt, then where could help be found? If they, the chosen ones, became selfish, if they wrangled about who should be greatest, then the fire which our Lord had come to send upon earth was clearly not burning in them, and whence could it be kindled afresh? — Wuest, page 193.

The words “And every sacrifice will be seasoned with salt” were probably not in the original manuscripts but were added in an attempt to make sense of the passage.

Have salt in yourselves (v.50) — Keep the seasoning power, the preserving, sacrificial Fire, within your hearts, and as first condition of its presence there, be at peace with your brethren. Thus, the discourse reverts to the point from which it started (v.33). Disputes about precedence endangered the very existence of the new life. — Wuest, page 193

it (v.50) — Greek makes it clear this is referring to the salt itself.

The salt of the illustration was salt from the Dead Sea which, unlike modern salt, contained impurities which made it lose its saltiness. — Thomas, page 126.