We notice also that Jesus said that the number of such self-proclaiming believers, who are not really regenerate, is declared to be “many.” This should elicit caution in our assumptions of the success of our methods and techniques of evangelism. We tend to be quite sanguine with our “evangelism statistics” when we assume the conversion of all who answer an altar call, make a “decision for Christ,” or recite the “sinner’s prayer.” These tools can help measure outward professions, but they do not give us a glimpse into the heart. All we can ever see of a person’s profession is his fruit. And even the fruit can be deceptive. God, and God alone, can read the human heart. Our gaze cannot penetrate beyond the outward appearance.
R.C. Sproul