Evangelism Involves Teaching
A passage from Ray Comfort's excellent book, The World's Greatest Preachers, p.173:
"It is obvious from Scripture that God requires us not only to preach to sinners, but also to teach them. The servant of the Lord must be 'apt to teach, patient, in meekness instructing' those who oppose him (2 Timothy 2:24-25). For a long while, I thought I was to leap among sinners, scatter the seed, then leave. But our responsibility goes further. We are to bring the sinner to a point of understanding his need before God. Psalm 25:8 says, "Good and upright is the Lord: therefore will he teach sinners in the way." Psalm 51:13 affirms, "Then will I teach transgressors thy ways: and sinners shall be converted unto thee." The Great Commission is to teach sinners: "Teach all nations...teaching them to observe all things" (Matthew 28:19-20). The disciples obeyed the command: "Daily in the temple, and in every house, they ceased not to teach and preach Jesus Christ" (Acts 5:42, emphasis added). The "good-soil" hearer is he who "heareth...and understandeth" (Matthew 13:23).
Philip the evangelist saw fit to ask his potential convert, the Etheopian, "Do you understand what you are reading?" (Acts 8:30 NKJV). Some preachers are like a loud gun that misses the target. It may sound effective, but if the bullet misses the target, the exercise is in vain. He may be the largest-lunged, chandelier-swinging, pulpit-pounding preacher this side of the book of Acts. He may have great teaching on faith, and everyone he touches may fall over, but if the sinner leaves the meeting failing to understand his desperate need for God's forgiveness, then the preacher has failed. He has missed the target, which is the understanding of the sinner. This is why the Law of God must be used in preaching. It is a ""schoolmaster" (Galatians 3:24-25) to bring "knowledge of sin" (Romans 3:20). It teaches and instructs. A sinner will come to "know His will, and approve the things that are most excellent" (see Acts 22:14; Philippians 1:10), if he is "instructed out of the Law" (Romans 2:18)."
Don't just preach the Gospel. Make sure your hearers are understanding it.