That phrase comes from the Bible—specifically Matthew 5:13 in the Sermon on the Mount. The fuller line is: “Ye are the salt of the earth: but if the salt have lost his savour, wherewith shall it be salted?”

Meaning in Context

• Salt as value or influence: In the ancient world, salt was essential—not only for seasoning but also for preserving food. Calling someone “the salt of the earth” meant they were valuable, steady, and life-preserving.

• Losing savor: If salt loses its flavor or potency, it becomes useless—it can’t fulfill its purpose anymore.

• The rhetorical question: “Wherewith shall it be salted?” means: if salt loses its unique quality, there’s nothing else that can restore it. It’s a warning that once you lose your essential character or purpose, you risk becoming ineffective.

Broader Interpretation

• Spiritual/moral lesson: Followers are meant to live in a way that preserves goodness and adds meaning (like salt adds flavor). If they abandon that, they lose their distinctive role.

• General usage today: It’s often used to describe the importance of staying true to one’s principles or maintaining integrity, because once that’s gone, it’s hard—or impossible—to recover.

Would you like me to also explain how this phrase has been used historically in everyday English (outside the religious setting)?

(http://www.autoadmit.com/thread.php?thread_id=5763560&forum_id=2/en-en/#49193583)