James 5:15 "And the prayer of faith will save the sick, and the Lord will raise him up. And if he has committed sins, he will be forgiven."

In this passage of scripture, the Holy Spirit speaks about the prayer of faith. And He speaks about the certainty of the outcome of this type of prayer. For in this passage, the Holy Spirit tells us categorically, that the prayer of faith will (not might) heal the sick (the word translated "save" more correctly means "heal") and even if sin in the life of the believer was the cause of their sickness, God would forgive their sin. And so, we see from this passage of scripture, that the prayer of faith, when applied correctly, will always produce the desired outcome.