—Jesus (Matthew 5:13)
This verse is popular enough to be familiar even to non-Christians. It's one of many that sounds a bit harsh, if only because the consequences of not acting like who Jesus has declared us to be are indeed grave.
Salt's qualities make the implication of Jesus' initial statement clear: it flavors, it preserves, and it is to be rubbed into and throughout a piece of meat in order to be most effective. A big chunk of salt laying on top of the meat isn't really doing its job, and it tastes awful.
Part of what's made Jesus' warning seem harsh to me in the past is the fact that I've personalized it and tried to gauge myself against it as an individual. Am I measuring up? What if I'm not? Will I be thrown out and trampled on?
I wonder if the key to understanding this better, however, is His context. He's speaking to a community, and perhaps He is also speaking about this community. When I consider much of current Western Christian culture, something in my mind begins to say, "Aha!" Corporately, how's our taste? Honestly, I think it is either bland or repulsive at least as often as it is good. Are we rubbed into the meat, yet staying salty? Much of the time, we're either in our own (sometimes huge) clusters doing our Christian thing or content with being an unflavored part of the mass except in our Bible studies, prayer meetings, and worship services (if we do those things at all, because hey, life is busy!).
So how should the world respond to our presence? Indeed, there are many ways in which today's Christian culture is "no longer good for anything except to be thrown out and trampled under people's feet." Much of "Christian" literature, music, art, thought, politics, etc. should be thrown out and trampled—that's a right response to its quality and content.
An example: Seeing The Chronicles of Narnia: The Lion, the Witch, and the Wardrobe was a mixed bag for me. I think many key moments were sidetracked or watered down, Aslan was dialed down a few notches, and there was little regard to the point of any of it. That said, I shuddered when I thought of what kind of movie Christians would have produced—it would have been so much worse.
I'm not sure how we lost our taste, but I think honesty about that is a prerequisite to seeing it restored.