I love The Message’s paraphrase of this passage:
Let me tell you why you are here. You’re here to be salt-seasoning that brings out the God-flavors of this earth. If you lose your saltiness, how will people taste godliness? You’ve lost your usefulness and will end up in the garbage.
Here’s another way to put it: You’re here to be light, bringing out the God-colors in the world. God is not a secret to be kept. We’re going public with this, as public as a city on a hill. If I make you light-bearers, you don’t think I’m going to hide you under a bucket, do you? I’m putting you on a light stand. Now that I’ve put you there on a hilltop, on a light stand—shine! Keep open house; be generous with your lives. By opening up to others, you’ll prompt people to open up with God, this generous Father in heaven.