Some people may wonder if using the Law (the Ten Commandments) in evangelism produces legalism. When the Law is used to show a sinner that sin is “exceedingly sinful”—that nothing can commend him to God—he clings to the cross knowing that he is saved by grace and grace alone.
This knowledge gives the Christian the understanding that even after a lifetime of good works, fasting, praying, seeking the lost, etc., his “works” don’t commend him to God—he is still saved by grace and grace alone. However, when the Law isn’t used before the cross, and a sinner simply makes a “decision for Christ,” he comes with a lack of understanding about the true nature of sin. After his commitment, he thinks that his good works, his fasting, praying, evangelism, etc., commend him to God. He is the one who thinks that what he eats, what he wears, and what he does become relevant to his Salvation. He is the one who is liable to say “touch not, taste not, handle not”—the one who becomes “legalistic.” Using the Law in evangelism before the cross liberates a new convert from legalism.