How Sin Works

The law discourages us because it shows us the holiness of God; it shows us the deceitfulness of sin within us, it pin-points it; it brings it out; aggravates it and so stimulates it in us. It tells us not to do something and in telling us that it introduces us to it and arouses within us a desire to do it. The law cannot save us or deliver us.
This is why moral teaching alone to unbelievers is insufficient. It’s complete nonsense to believe that you can teach young people not to commit sin by merely telling them about the evil consequences of sin. What you are doing is to introduce them to the pleasures of sin. That’s the effect moral teaching generally produces. In telling them not to sin you are giving them a picture of the thing and at once they desire it. The basic passions and lusts are stronger than our minds. That’s how sin works.
Here’s a person under law. They are helpless, depressed and discouraged, and the more the law tells them not to do certain things the more they desire to do them. Isn't that what every child does? Tell them not to do something and immediately they want to do it. That’s human nature. Sin twists all the commandments and makes us worse than we were before. That's why we need a savior that's why we need grace.