It’s possible to over-exegete this passage, in my opinion, and look too much at the various uses and characteristics of salt. As I look at this in the context of the Sermon, I see it pretty simply.
Salt makes food taste better.
When the food is salted just right we don’t say, “That’s good salt.” We say, “That’s good food.”
Salt simply is hidden in the food and makes it taste better. We are the salt of the earth.
A lamp is a source of light for those in the vicinity. We don’t look at the lamp. We read our book or write in our notebook or look at our pictures.
Light makes the vicinity usable. We are the light of the world.
Let us hide ourselves and call attention to Jesus.