We are told in the Bible that after Adam and Eve sinned they knew both good and evil. They and their descendants now had an inward knowledge of right versus wrong. The Bible calls this – conscience, and explains that every person shows the work of the law written in their hearts, their conscience also bearing witness.
Conscience is a moral compass that God has given to every person. Here is a simple way to use conscience when witnessing. Ask someone “Do you consider yourself a good person?” The Bible tells us: “Every way of a man is right in his own eyes,” so they usually say yes. Then ask if you can review a few of the Ten Commandments to determine their goodness. Ask them, “Have you ever told a lie – even a small one? Have you ever been greedy even once? Have you ever taken you’re Creator’s name in vain? Have you always put God and His Word first?” Once they confess to breaking God’s law, ask if they think God will let Liars, Covetors, Blasphemers, or Idolaters into heaven. Though they will be uncomfortable and may make excuses, this is critical. Only a person who knows he is hopelessly lost will seek the Savior.
We have produced a video called The Good Test that uses this approach. Watch it free on our website to get the idea, and then find a sinner a give it a try. The Ten Commandments are foundational, convicting, and lead to the Savior.