'Salt' symbolizes the desire of truth and good to be conjoined with each other. So, a salt can conjoin water, which corresponds to truth, with oil, which corresponds to good.

Salt can also have a negative meaning. 'Lot's wife becoming a statue of salt' signifies all the good of truth being vastated, or laid waste, in the church that Lot represented. In that story, Lot's wife represented a form of 'truth' that turned itself away from 'good,' and looked instead to doctrinal matters. Because 'salt' can signify vastation, and 'cities' signify doctrinal aspects of truth, in old times they sowed cities with salt when they were destroyed to prevent them from being rebuilt, as in Judges 9:45

(References: Arcana Coelestia 10300)

10301. 'Pure' means devoid of evil. This is clear from the meaning of 'pure' as devoid of evil. Because all evil is impure, and all good is pure, the expression 'being purified' from sins and from iniquities is used. And it has regard to the heart, that is, the will; for the will is meant in the Word by 'the heart', 2930, 7542, 8910, 9300, 9495, since love is meant by it, 3883-3896, 9050.