What danger does Les see in ministry success?
Ministry success carries the danger of pride, described as getting the big head. The moment a servant thinks he can accomplish the work himself, he is done. Christian service must be carried out as a weak vessel whom God has seen fit to use, not through self-confidence or personal ability.
Les explains that success in ministry is dangerous because it can produce pride—getting the big head. He welcomes reminders that unless the Lord blesses the ministry, the servant must not become proud, and he says that is always a danger. The minute a person thinks he can do it himself, he is all done. Christian service must instead be done as a weak vessel God has seen fit to use. This fits the surrounding discussion of Paul's thorn, which kept him humbled, and God's word that His grace is sufficient and His strength is made perfect in weakness.