The conundrum was solved by Kevin. Kevin usual knows. He's a great reader. Kevin said salt was used in making ovens because it held heat (think salting ice on roads). People made their oven. Then they put a layer of salt across the floor of the oven. Tile was placed over the salt layer. Now the oven held the heat. Eventually, the salt's ability to hold heat lessened and was gone. Then the salt was "no longer good for anything but to be thrown out and trampled underfoot." Matt 5: 13.
Jesus is telling us not to lose our "flavor." Glorify God by being His disciple and seasoning others with Christ's flavor. A little salt makes the food taste better.