Physics recognizes the second law of thermodynamics. Everything is winding down. Everything atrophies. Everything decays unless it’s maintained.
Do you have a car? The clutches and seals in the transmission will wear out. Own a home? The siding will rot. The mortar in the bricks will need touching up. The porch will sag. The plumbing will stop up. Have a computer? Its CPU will crash if you don’t maintain it.
What most of us don’t realize is that there is a spiritual version of that law. It’s called “the law (or doctrine) of total depravity”. It means that the whole person is affected by something that destroys us, something that causes problems in our relationships and our communities. The mind, the will, the emotions and the body of every human being is infected with a condition known as sin. It doesn’t mean that everyone is as bad as he can possibly be. It means that left to ourselves, without something to keep us in line, we will tend toward selfish, greedy and destructive behavior.
The second law of thermodynamics means we must work at maintaining physical things. The law of total depravity means that we must work at maintaining spiritual things. That’s what Jesus meant when he said, “You are the salt of the earth. But if the salt has lost its saltiness it is good for nothing but to be thrown out and trampled under foot by men. You are the light of the world. A city set on a hill cannot be hidden. Neither do men light a lamp and put it on under a basket, but on the lamp stand, and so it gives light to all who are in the house.” (Matthew 5:13-16).
How to pull that off? Well, it can be costly. The late Howard Hendricks told this story:
Recently, I was walking the streets in San Mateo, California. I met an attorney I knew from a local evangelical church. I said to him, “What are you doing?”
He said, “I’m looking for a job.”
I said, “You’ve got to be kidding.”
He said, “No, last week I walked out the front door of that corporation and told them, ‘You can hang it on your beak. I’m no longer going to write contracts that you and I both know are illegal and illegitimate.'”
That man is regarded as one of the top five corporate lawyers in America, and he’s unwilling to sell his value system for a mess of pottage. We need a larger core of lawyers like that.
I can hear you thinking, “Yeah, we need more lawyers like that!” But to be honest we need more mechanics, more doctors, more contractors and more everybody to be like that. That’s what it means to be salt.
Without something to preserve it, the world will suffer ethical decay. Without something to light the way, the world will recede into darkness. God put his church into the world to be that something. God put you and me here to do something for the world that the world cannot do for itself. You are the salt of the earth. You are the light of the world.
 Citation: Howard Hendricks, “Beyond the Bottom Line,” Preaching Today, Tape No. 101