The Phrase Finder explains that the expression refers to those “…of great worth and reliability.” The expression was mentioned in the King James version of the Bible in Mathew 5:13. Perhaps the most interesting aspect of the expression is that its meaning is in conflict with the fact that salt was spread on the land to poison it for growing crops in the Middle Ages “…as a punishment to landowners who had transgressed against society in some way.” The positive connotation of the expression was instead based on the value of salt. The powerful were “above the salt” and valued workers were “worth their salt.”