And even if our gospel is veiled, it is veiled only to those who are perishing. In their case the god of this world has blinded the minds of the unbelievers, to keep them from seeing the light of the gospel of the glory of Christ, who is the image of God. For what we proclaim is not ourselves, but Jesus Christ as Lord, with ourselves as your servants for Jesus’ sake. For God, who said, "Let light shine out of darkness," has shone in our hearts to give the light of the knowledge of the glory of God in the face of Jesus Christ. – 2 Cor 4:3-6
There are a couple of important ‘keys’ to effective evangelism in those passages.
The first one has to do with ‘knowing your audience’. For anyone accustomed to teaching/speaking this is an essential ingredient for being effective. In these passages we are told by the Apostle that our ‘audience’ contains unbelievers with ‘blind’ minds, and can’t see!
Why in the world would we want to deliver a message to a blind audience? That makes no sense!
What did Paul do? If we have read our Bibles, we find that everywhere Paul travelled, he preached a simple gospel that Christ died for sins, knowing that he was speaking to a blind audience, that would find his message offensive! At the same time, Paul knew that there would be those who would repent and believe the gospel he preached. How did he know that?
That’s the other key to effective evangelism in the above verses. For Paul knew that God would open blind eyes as he preached the gospel and souls would be saved.
The summary of evangelism is this:
We faithfully preach Christ;
God opens blind eyes;
God-opened blind eyes, deaf ears, and softened hearts respond;
. . .and the Church of Christ is built..