James 3:9 "With the tongue we praise our Lord and Father, and with
it we curse men, who have been made in God's likeness. Out of the
same mouth come praise and cursing. My brothers, this should not be.
Can both fresh water and salt water flow from the same spring? My
brothers, can a fig tree bear olives, or a grapevine bear figs?
Neither can a salt spring produce fresh water."
Reading salt as a positive thing here in James is somewhat
problematic. In Greek, James uses the word for "bitter" for sea
water. Then in 3:14 he refers to the "bitterness of jealousy" using
the same Greek word. On the other hand reading "salt" as a positive
makes his point better. His overall theme in the letter is that we
must show fruits of the goodness inside us. And immediately before
he refers to salt, he is saying that bad things should not come out
of us. It would make more sense then to say "good cannot produce
bad" than to say "bad cannot produce good". We don't know how well
James's first audience knew the metaphor of salt as a good thing.
But, if we assume they did know it well, then James would have
written "sea water" with confidence that his message would be
understood with salt as a positive. James then immediately turns
this meaning around.
I think what is going on here is that both the author of James and
his audience are familiar with "salt" as a positive as used in Mark.
An opponent of the author of James, Paul perhaps, has also used the
salt sayings as found in Mark to argue against the need for works.
The case against works could be made from Mark since the salt in
Mark is an internal quality. The author of James is arguing against
this position, and it helps his case to turn the metaphor around. If
both Paul and the author of James are arguing different
interpretations of the salt sayings from Mark, then this would make
the date of the original Mark or at least the source for the salt
metaphors in Mark fairly early.