For Christ did not send me to baptize but to preach the gospel, not in cleverness of speech, lest the cross of Christ be emptied of its effectiveness. (1 Corinthians 1:17)
In the Corinthian culture, eloquent speakers enjoyed high status in the community - almost like sports heroes or movie stars today. Their message was less important than the way they presented it.
By contrast, the good news of Christ's sacrificial love was much greater than the one who delivered it. In fact, as Paul writes, a polished presentation of the gospel ran the risk of diminishing its power.
You don't have to be an effective communicator to share your faith. In fact, it can sometimes get in the way. The Christians who have most shaped my walk with Christ have not been preachers or professors, but simple believers who told me about Christ's love and what God had done in their lives - in their own words.
Marion Soards puts it this way -
"The cross is not a pretty sight, and sheer manipulative eloquence is not a medium that can bear the weight of the message of Christ's cross."