As Christians, we are called to be salt and light. The statement still rings true today despite the many changes in culture. The problem is, due to the advancement of technology, the many uses of salt have fallen by the wayside. The age of refrigeration has rendered the need for salt as a preservative null and void. The real question is: has the Biblical application for being salt become null and void?
Most teachings out there regarding salt come from chefs who are preachers (or preachers who are chefs, depending on where their true passion lies) or have a friend who is a chef and was inspired by a conversation with them. Either way, the popular teaching generally revolves around salt being a flavoring agent, and how we as Christians need to make the world "taste" better. Sadly, not only is it culinarily inaccurate, but also theologically lacking.
The thing is, salt isn't a flavor, it just brings out the flavor that already exists in the food. If you eat salt, it will just taste salty, duh! However, if you put salt on French fries, you wind up tasting more of the potato than before. Salt requires something to work with it, otherwise it's useless. Without that fried potato, salt is a waste of eating!
Not only does salt bring out the good things, but also the bad things. The way it interacts with your taste buds, it amplifies whatever it is you're tasting. So it could be a delicious French Fry, or it could be a piece of rotten fish. You'll find out the true nature very quickly by salting things properly.
Likewise, if we're living as Christians in this world, we will naturally bring out the true nature of the world around us. Like the rotten fish, it's not always a good thing bringing out the true nature of people in this world. Nevertheless, it's Biblical and most necessary to do so. You see, how we share Jesus with the world will draw forth a response of some sort. The other person's response shows who they really are. For instance, someone could say they're a Christian, yet cuss you out for talking about hell. Obviously, there's an issue they have to work out if they're responding that way, and you wouldn't have known if it hadn't happened. If you didn't know, you wouldn't have done anything about it.
In conclusion: being a follower of Christ will bring forth responses from the world. Those responses will help you discover their true nature and figure out how to treat them.
"Let your speech always be with grace, seasoned with salt, that you may know how you ought to answer each one." Colossians 4:6