Matthew 5:14-16 KJV
14 Ye are the light of the world. A city that is set on an hill cannot be hid. 15 Neither do men light a candle, and put it under a bushel, but on a candlestick; and it giveth light unto all that are in the house. 16 Let your light so shine before men, that they may see your good works, and glorify your Father which is in heaven.
When we become children of God by accepting Christ's free gift of salvation, we become light to the world. We are to shine for Jesus. We are to share Him with others so they can come to know HIm, too. We can not hide our lights.
First, we couldn't even if we tried because light overtakes darkness. Secondly, what good is a light that doesn't reach those around it? We must share Jesus!