meaning of "salted among the ranks of"
The Berrys had been blessed, their last owner, Lucius Berry, being one of the rare true Christians salted among the ranks of the so-called faithful. Lucius’s parents and siblings had died in the 1832 cholera epidemic, leaving him sole ownership of the family tobacco farm and the seven human beings who worked it. Interpreting the epidemic as divine confirmation of what his conscience already knew, Lucius set out to atone for his family’s sin: He sold off the rest of his inheritance, put his slaves into wagons, and escorted them safely out west, where he gave them not just their freedom but money and land to make a new start. Proving that such an act was indeed possible.
Can anyone tell me what 'salted among the ranks of' means in here?
While I could not find a source confirming this particular interpretation, I'd argue that it means something like scattered among. The author says that most of the faithful are just "so-called", and that the genuine Christians among them are rare. This expression seems to be a way of comparing them to grains of salt that have been lightly dispersed among them only here and there, as real grains of salt might be from a salt cellar.
It might well carry overtones of the biblical passage from Matthew, although it does seem to be focused primarily on the quality of Christians and their faith, as opposed to their prevalence in the population.
For example, Wikipedia, already cited by others, notes that, "The most common interpretation of this verse [Matthew 5:13, "salt of the earth"] is a reference to salt as a preservative, and to thus see the duty of the disciples as preserving the purity of the world."
Again, the passage cited by the OP seems focused on the rarity of genuine Christians and not on the nature of their faith. Hence, an interpretation as scattered among makes sense here.
It seems to be an extension of either
1
- transitive. c. To sprinkle (snow) with salt in order to melt it; to sprinkle (a roadway) with salt in order to melt snow or ice. (OED)
Where to salt = to sprinkle
and
2 the method of seasoning, i.e. sprinkling
5.a. figurative. To season; 1895 G. Meredith Amazing Marriage I. ii. 22 He salted his language in a manner I cannot repeat; no epithet ever stood by itself.
To sprinkle - to scatter randomly.