The following is taken directly from the Evidence Bible
The Evidence Bible (easy reading “comfort-able KJV”) pg1308
The Key to Reaching the Lost
Have you ever thought, “There must be a key to reaching the lost”? There is -and it’s rusty through lack of use. The Bible does actually call it “the key,” and its purpose is to bring us to Christ, to unlock the Door of the Savior (John 10:9 ~ Yes, I am the gate. Those who come in through me will be saved. They will come and go freely and will find good pastures)
Much of the church still doesn’t even know it exists. Not only is it biblical, but it can be shown through history that the Church used it to unlock the doors of revival. The problem is that it was lost around the turn of the twentieth century. Keys have a way of getting lost.
Jesus used it. So did Paul (Romans 3: 19,20~ 19Now we know that what things soever the law says, it says to them who are under the law:that every mouth may be stopped, and all the world may become guilty before God. 20Therefore by the deeds of the law there shall no flesh be justified in his sight: for by the law is the knowledge of sin.) Timothy (1 Timothy 1: 8-11~ 8We know that the law is good when used correctly. 9For the law was not intended for people who do what is right. Is is for people who are lawless and rebellious, who are ungodly and sinful, who consider nothing sacred and defile what is holy, who kill their father or mother or commit other murders. 10The law is for people who are sexually immoral, or who practice homosexuality, or are slave traders, liars, promise breakers, or who do anything else that contradicts the wholesome teaching 11that comes from the glorious Good News entrusted to me by our blessed God.) and James (James 2:10~ For the person who keeps all of the laws except one is as guilty as a person who has broken all of God’s laws.) Stephen used it when he preached (Acts 7:53~ You deliberately disobeyed God’s law, even though you received it from the hands of angels.) Peter found that it had been used to open the door to release 3,000 imprisoned souls on the Day of Pentecost. Jesus said that the lawyers had “taken away” they key, and refused to use it to let people enter into the kingdom of God.
The Pharisees didn’t take it away. Instead, they bent it out of shape so that it wouldn’t do its work (Mark 7:8~ “For you ignore God’s law and substitute your own tradition.” ) Jesus returned it to its true shape, just as the Scriptures prophesied that He would do (Isaiah 42:21~ The Lord is well pleased for his righteousness’ sake; he will magnify the law, and make it honourable.)
Satan has tried to prejudice the modern Church against the key. He has maligned it, misused it, twisted it, and, of course, hidden it -he hates it because of what it does. Perhaps you are wondering what this key is. I will tell you. All I ask is that you set aside your traditions and prejudices and look at what God’s Word says on the subject.
In (Acts 28:23~ So a time was set, and on that day a large number of people came to Paul’s lodging. He explained and testified about the Kingdom of God and tried to persuade them about Jesus from the Scriptures. Using the law of Moses and the books of the prophets, he spoke to them from morning until evening.) the Bible tells us that Paul sought to persuade his hearers “concerning Jesus, both out of the law of Moses, and out of the prophets.” Here we have two effective means of persuading the unsaved “concerning Jesus.”
Let’s first look at how the prophets can help persuade sinners concerning Jesus. Fulfilled prophecy proves the inspiration of Scripture. The predictions of the prophets present a powerful case for the inspiration of the Bible. Any skeptic who reads prophetic words of Isaiah, Ezekial, Joel, etc., or the words of Jesus in Matthew 24 cannot but be challenged that this is no ordinary book.
The other means by which Paul persuaded sinners concerning Jesus was “out of the law of Moses.” The Bible tells us that the Law of Moses is good if it is used lawfully (1 Timothy 1:8_refer above for verse). It was given by God as a “schoolmaster” to bring us to Christ (Galations 3:24~ Let me put it another way. The law was our guardian until Christ came; it protected us until we could be made right with God through faith.) Paul wrote that he “had not known sin, but by the law” (Romans 7:7~ Well then, am I suggesting that the law of God is sinful? Of course not! In fact, it was the law that showed me my sin. I would never have known that coveting is wrong if the law had not said, “You must not covet.”) The Law of God (The Ten Commandments) is evidently the “key of knowledge” Jesus spoke of in (Luke 11:52~ What sorrow awaits you experts of religious law! For you remove the key of knowledge from the people. You don’t enter the Kingdom yourselves, and you prevent others from entering.” ) He was speaking to “lawyers”-those who should have been teaching God’s Law so that sinners would receive the “knowledge of sin,” and thus recognize their need for the Saviour.
Prophecy speaks to the intellect of the sinner, while the Law speaks to the conscience. One produces faith in the Word of God; the other brings knowledge of sin in the heart of the sinner. The Law is the God-given “key” to unlock the Door of Salvation.
“I do not believe that any man can preach the gospel who does not preach the Law. The Law is the needle, and you cannot draw silken thread of the gospel through a man’s heart unless you first send the needle of the Law to make way for it.” Charles Spurgeon
NOTE: The above Bible verses in red are taken from either the Evidence Bible or The Life Application Study Bible by Tyndale (New Living Translation) 
