Worth one's salt.

Worth one's salt.

Meaning

To be effective and efficient; deserving of one's pay.

Origin

Sodium chloride, a.k.a. salt, is essential for human life and, until
the invention of canning and refrigeration, was the primary method of
preservation of food. Not surprisingly, it has long been considered
valuable.

To be 'worth one's salt' is to be worth one's pay. Our word salary
derives from the Latin salarium, (sal is the Latin word for salt).
There is some debate over the origin of the word salarium, but most
scholars accept that it was the money allowed to Roman soldiers for
the purchase of salt. Roman soldiers weren't actually paid in salt, as
some suggest. They were obliged to buy their own food, weapons etc.
and had the cost of these deducted from their wages in advance.

Salt continues to be important enough to feature in the language for
many centuries. Other phrases that would have been known to the
mediaeval mind were take with a grain of salt, the salt of the earth
and below the salt. The ancient roots of 'worth one's salt', and its
similarity to the 13th century 'worth one's weight in gold' and the
14th century 'worth one's while' (i.e. worth one's time), give the
phrase a historical air. Nevertheless, 'worth one's salt' didn't exist
in Roman Latin or even in mediaeval English and dates from as recently
as the 19th century.

The earliest citation of the phrase that I have found in print is in
The African Memoranda, a report of an expedition to Guinea Bissau, by
Philip Beaver, 1805:

"Hayles has been my most useful man, but of late not worth his salt."

It's worth pointing out that, although English is replete with phrases
of a nautical origin, none of the above salty phrases has anything to
do with the sea.