Salt is used by Jesus as an example of a seasoning, not as an example of a preserver
I have heard many preachers use the salt parable as an example of a preserver, ascribing the paternity of this simile to Jesus' words. However, this is not so. Jesus never used salt as an example of a preserver, but as an example of a seasoning. Even though I don't think this mistake has doctrinal o interpreting implications, I will clarify it anyway, for the sake of truth.
This figure of speech appears only three times in the Bible, and in all three times it is used referring to savor or seasoning, never as a preservative. Let's take a look at Matthew 5: 13; Mark 9: 50 and Luke 14: 34.
"Ye are the salt of the earth, but if the salt have lost his savour, wherewith shall it be salted? it is thenceforth good for nothing, but to be cast out, and to be trodden under foot of men." ( Matt 5: 13 )
In this verse we have just read, Jesus asked what would happen if the salt lost its savour, not about what would happen if the salt lost its preserving power. The focus is in the taste, not in any other characteristic of salt. This is also taught in a similar fashion in Mark 9: 50; let's read.
"Salt is good, but if the salt have lost his saltness, wherewith will ye season it? Have salt in yourselves, and have peace one with another." ( Mark 9: 50 )
In this verse just read, it is even more clear that the characteristic of salt is mentioned not because of its preservative power, but its seasoning quality. This fact becomes evident when we read the word "season" regarding to the parable. It becomes even more evident in Luke 14: 34, where both words: "savour" and "season" are used.
"Salt is good, but if the salt have lost his savour, wherewith shall it be seasoned? ( Luke 14: 34 )
Because of what we have analyzed in all three verses where this parable is mentioned, I don't ascribe to salt, in this parable, its preserving characteristic, but rather its characteristic of seasoning. Therefore, this parable shouldn't be presented in a way different from what Jesus presented it.