Light does at least three things:
1. It warns.
2. It directs.
3. It reveals.
In all three cases, the light is shining. That's what light does--it shines.
Think of being out in a small motorboat in the ocean late at night. No navigation equipment. You look over and see a lighthouse.
1. It warns you that as you get closer you will be near rocks so be careful.
2. It directs you towards land.
3. It reveals anything else around you that it's light reflects off of.
Jesus said, "I am the light of the world." (John 8:12) Jesus warns us that He will be back and that there is a judgment (on sin) for all who haven't trusted Christ yet. Before that there is a judgment for His followers (on their works or lack thereof) as well.
Jesus also directs us. "Follow me" is for all those who trust Jesus.
Jesus reveals truth. He exposes evil deeds done in darkness. John 1:5
The light shines in the darkness, but the darkness has not understood it.
Finally, Jesus tells us, "You are the light of the world." Matthew 5:13-15
In other words, we are to shine.
Therefore, to shine, we should warn others that we'll stand before God, direct them to Jesus (who is the way, and the truth, and the life), and reveal Jesus and His truth and love the others as His ambassador.
What a high calling we have. May God give us the faith and courage to follow through.
Are you shining?