Obedience to His Will is the active part of my faith. Those who are faithful to God in every way realize that this is important IF we want to attain heaven. We know the Will of the Father through His revealed Word. What here is meant is that Christians are the preserving power. Note some Illustrations that show the usage of salt as a preservative.
Salt also creates thirst.
The basic work of light is to take away darkness. Our difference should be seen in the way people act about us. The way the speak, joke etc. The environment should be purer and not dirtier. Paul in Jail.