Perhaps one of the most common examples poor exegesis is the use of 3 John 2, usually quoted in the King James: “Beloved, I wish above all things that thou mayest prosper and be in health, even as thy soul prospereth”. This is a favorite among extreme prosperity preachers. By misunderstanding this verse, one could say “…if my soul is prospering, then I should prosper by default in my money and body.”
I do not believe this was John’s point. This was a common ancient greeting. Basically, I believe John is saying “May all go well with you, inside and out”. In fact, this verse is bookended with statements concerning “the truth”. In vs 1, he says “I love you in the truth”. In the following vs, John mentioned “faithfulness to the truth” and “walking in the truth” and the same statement in vs 4 again. Perhaps, this was on John’s mind, much more than money. Though to be clear, I do believe God prospers us financially, taking care of all our need (Phil 4:19).
The danger in the above example would be thinking that if I’m doing well spiritually, I will do well financially, that I will be rich with no exceptions. This is not supported in the larger context of the Bible at all. It is certainly not supported in 3 John. This could cause damage to a Christian, especially a new one. If they go through a hard time, which is normal in the Christian experience, he/she may become disillusioned and perhaps be tempted to give up. We would not want that.