What's the reasoning behind the metaphorical expression "as still as salt"?

[Jamee Zhao]

Jamee, as for yourself and Jaleel10, I have never before encountered the expression “as still as salt”; nevertheless, as salt is an inanimate substance, I fully agree that its presence in the phrase “as still as …” evokes calmness, tranquillity, quietness, lifelessness and the like.

J.M. Barrie may have learned this otherwise remote expression in his youth in Scotland or, as an very imaginative writer, he could have just as easily devised it himself. He was known to play with the language as in “’Curiouser and curiouser’ cried Alice.”

Most languages are pervaded by thousands of popular metaphors, aphorisms, colloquiums, and idiomatic expressions the meanings of which, for a native-speaker, are often immediately clear upon first encounter. The authors of these flavourful particles are rarely credited.

As an aside, your ability to grasp the works of J.M. Barrie suggests to me far too much modesty in your self-evaluation as a “beginner” in English.

EDITED:
Typos!
Tinkering.

Thank you. I actually have learned English for thirteen years, but as I can say now, the progress is not so satisfactory. I can read and listen well, but made slow progress in writing and speaking, and that's why I evaluate myself as a beginner in English. Besides, as the language learning process is endless, it will give me strong motivation to keep going without burden when I label myself a beginner

[drmweaver2]

Well, for me, "the congregation of the dead" followed by the "as still as salt" seems like a long, double metaphor which made me think of how people used to be covered/preserved in salt at one time. (The salt acts as a dessicant.) In any case, both dead people and "salt flats" are still - unmoving and silent, both meanings of "still".

Actually, the religious "origin" was something I didn't even have a clue about until someone mentioned it earlier in the thread. Since then that association has become cemented for me by finding the Internet reference I quoted.

[Cainntear]

My first thought (before finding out it was a Scottish phrase) was that it might have something to do with salt flats, which can look like lakes or seas from the edge, but don’t move. But we don’t have any salt flats here, so it can’t be that!!