"You are the light of the world. A town built on a hill cannot be hidden. Neither do people light a lamp and put it under a bowl. Instead they put it on its stand, and it gives light to everyone in the house. In the same way, let your light shine before others, that they may see your good deeds and glorify your Father in heaven."
To me, this verse means that we're supposed to do more than just exist. God didn't create us just to take up space on earth, He wants to use us to make a difference in His kingdom. We have a purpose.
Whenever I walk into my bedroom at night, and my little sisters are already asleep, I can't see anything, but when I turn on my ipod, it lights up so that I can see enough to know where to walk. In the same way, in a dark world full of sin, we are the light, pointing people on the path to Jesus. If we are Christ-followers, our candles shouldn't be burned out and dark just like those who aren't Christians, and we shouldn't hide our light either. We need to use it for the glory of the One who made us.
In the verse before that, Jesus calls us the "salt of the earth." Meaning that we're supposed to flavor up everything we do with a little bit of gospel. We're not supposed to be boring and flavorless, Jesus wasn't. He liked to spice things up by doing things that other people didn't necessarily agree with, but He did them because the Father said to.
We are called to stand out and be different, to make a difference. We're not supposed to be shaped and influenced by the world, but to go out and shape and influence the world.
So, think about it today. How can you make a difference in your world? What can you do to be the salt and the light?