You are the light of the world—like a city on a hilltop that cannot be hidden. No one lights a lamp and then puts it under a basket. Instead, a lamp is placed on a stand, where it gives light to everyone in the house. In the same way, let your good deeds shine out for all to see, so that everyone will praise your heavenly Father. - Matthew 5:14-16

I've taught on this passage several times in youth ministry.  It's a great illustration that Jesus gives regarding our responsibility to shine in the darkness.  This go around I wanted to do something different though, so I set out three objects: a light bulb, a picture of the moon, and one of those glow-in-the-dark stars you can put on your ceiling.

Then I went through something along these lines:

Light Bulb

This bulb, when illuminated, can light up a whole room.  But can this bulb, by itself, produce light?  No.  What does it need to shine?  (Answer - it needs to be plugged in to a power source.)

The Moon

The moon, when it's full, can be a source of light in the darkest night.  But does the moon, by itself, produce light?  No.  What does it need to shine?  (Answer - it needs to be tilted toward the sun so it can reflect its light.)

Glow-in-the-Dark Star

This star, when you turn off the lights, glows a comforting light.  But how does this star get its glow?  Does it, by itself, produce light?  No.  What does it need to shine?  (Answer - it needs to be in the light so it can absorb it and then re-emit it as it glows.)

Then you ask students something like this: now what about you?  Does a human being, by him/herself, produce light?  No.  What do we need to shine?  (We need God's presence, His power in our lives.)

Then you could ask students what item they think most represents us - are we more like the bulb, needing to be plugged in to the Source of power; are we more like the moon, we need to be turned toward God so we can reflect His light; or are we more like the star, we need to be in God's presence, absorbing His light so we can re-emit it?

When I did this with students, it was awesome!  Object lessons can be a powerful tool to use with your group, and every time a student sees a light bulb, one of those stars, or the moon, they may remember that they are called to be the light of the world!!!