Acts 8:30-40
The Ethiopian eunuch was an intelligent man. We know this because he was intelligent enough to oversee the treasury of an entire kingdom. We also know he was intelligent enough to recognize what he did not know. He was reading the book of Isaiah and he recognized that he did not understand all of it. When we believe we have the answer, we do not look for enlightenment. He knew what he did not know, and he was ready to have the text explained to him.
God knows the hearts and minds of people. He knows when they are receptive to hearing the truth of the gospel. The Holy Spirit did not explain Isaiah to the eunuch, instead he sent a Christian witness to do so; he sent Phillip. Phillip goes to the eunuch and asks him if he understands what he is reading, and the eunuch is humble enough to admit that he does not.
Starting with the passage that the eunuch was reading, Phillip told him the good news about Jesus. The eunuch responded with faith and Phillip baptized him. In all probability, the eunuch was the first gentile Christian. He returned home and took the gospel with him.
Phillip was able to use scripture as an effective method of sharing the gospel because the eunuch already respected scripture and believed it to be a source of godly truth. Witnessing is more effective when the Holy Spirit has been preparing the heart to receive the good news. Scripture is not a weapon that we use to hammer those in need of rescue. Scripture is a lifeline that we throw to those sinking in sin. Even when the person we want to help does not recognize the authority of scripture, the Holy Spirit will use it to speak to them.
Scripture reveals God; it is a revelation of his love, mercy and grace. The more effectively we can explain scripture, the more effective our witness will be. Christians who take witnessing seriously take Bible study seriously.