Matthew 5:16 Let your light so shine before men, that they may see your good works, and glorify your Father which is in heaven.
When many first world people read this passage they take a modern, generally incorrect, interpretation of the verse. That's because we live in a light rich world. Our light is generally fixed and switched. What I mean by that is most buildings and homes in our country have lights built into the structure which are controlled by switches. There is little to no maintenance or preparation for light to brighten the darkness in our world. If a light bulb is out we simply replace it with another bulb.
In the ancient world it was not that way. Lights were not often fixed and were never switched. Lights were fuel intensive, more scarce, and portable. There was planning, maintenance, and labor involved in piercing the darkness, and if the light shined bright and clear it was a testimony to the person responsible for the light. But if a light didn't shine it was a clear indication that the person who had responsibility for the light had failed in their duties. And a great failure it would be for the people who depended on the light. The longer and brighter a lamp burned the more work and maintenance it required.
This is how some ancients would have interpreted this passage. The “good works” would have been the planning, maintenance, and labor that were obvious when the light shined bright. The reason “the Father which is in heaven” would receive the glory is because he provided the materials and fuel for the light and also trained and maintained the light servant... so it is really His light.
The application then is obvious to all Christians. We are the light servants and have been commissioned by our master to give the light of truth to the world. If our light shines bright it is clear we have planned, maintained, and worked hard so the light would pierce the darkness and our Master, who is also our Father, would receive praise for the light. But what shame will be ours if the light doesn't shine bright.