Many people have night lights. Sometimes they plug them into a wall socket in their bathroom, so that there is a little light to guide you in the middle of the night. Sometimes they are in the hallway to guide you to your little children’s room when the cry comes in the wee hours of the morning.
Some people turn on outdoor lights at their houses at night to help keep burglars away. Burglars don’t like light! Often the lights are at the doors and at the corners of the house. Sometimes they are on a outbuilding. The lights are there to inhibit clandestine movement.
It wouldn’t make any sense to use these lights only in the daytime. The sun provides more than enough light to move and protect. It would make no sense to unplug them at night, or turn them off at night.
This first illustration Jesus uses to give us a glimpse at spiritual growth is about growth being visible. In Jesus day there were no nightlights you plugged into the wall to guide you at night. Instead they would use very small clay oil lamps, small enough to fit in the palm of your hand. The owner of the lamp would fill the reservoir with oil, trim the cloth wick, light it and bring it with them when they went to sleep. They would often place them under a bowl with one side of the bowl raised slightly by a rock or a stick. The result was that a dim light from the lit lamp would radiate on to the floor during the night.
We still measure light in terms of candles. One candle is roughly the total amount of light given off by a single lit candle. But we get only a small amount of one light of these oil lamp flames whispering out from under the crack. Not much light at all.
This nightlight under the bowl was not good for any function other than illuminating a small section of the floor. You couldn’t do any work by the light, since it didn’t radiate upward at all. It wasn’t enough to illuminate other objects or people in the room. It was only good for the one purpose of helping to prevent tripping or falling in the middle of the night.
During the day such a oil lamp would be place in a prominent place in the room to help see. Remember, this is before electricity and light with the flip of a switch. Even light from a window was limited, since glass was extremely rare, and bugs were abundant. Openings were kept to a minimum.
Artificial light sources have the purpose of illuminating objects. We turn on the light for our convenience and safety. Light takes the darkness away. The light of the Gospel dispels spiritual darkness. It makes no sense for us to hide this spiritual light from other people. It is meant to be seen.
The Arnold Journey 