I want to suggest an interpretation of this verse that Steve didn't reference on his verse-by-verse teaching on James.14 Is any one of you sick? He should call the elders of the church to pray over him and anoint him with oil in the name of the Lord. 15 And the prayer offered in faith will make the sick person well; the Lord will raise him up. If he has sinned, he will be forgiven. 16 Therefore confess your sins to each other and pray for each other so that you may be healed.
The tension here is that the passage SEEMS to indicate that if we pray in faith for a sick person, they will be healed, and yet many times people pray in faith and a sick person is not healed. Steve suggested, as an alternative, that the passage could be about unbelievers converting (an unbeliever gets sick, realizes his own mortality, calls for the church to pray him into the kingdom, and subsequently will be raised up in resurrection rather than dying in his sin).
I think, though, that the weight of the evidence still favors physical healing being in mind here.
My interpretation focuses on the phrase "In Faith"
These days, we tend to carry some modernist baggage to the term faith that wasn't necessarily present in the 1st century. We see faith as a blind leap. But James, I think, viewed 'faith' as a certain future. Well, in the proposed situation, what could have made the people praying certain that their prayers would result in healing (I, myself, don't think they interpreted Isaiah to mean that healing was guaranteed)?
I suggest that James may be thinking of a situation where a prophecy of healing has been uttered over the person in question. In other words, James means the following.
I know there are numerous option for interpreting this passage. But I have never heard this one and wondered what you guys think.14 Is any one of you sick? He should call the elders of the church to pray over him and anoint him with oil in the name of the Lord. 15 And the prayer offered in faith [If and only if God has revealed His will to heal in this case] will make the sick person well [God may heal w/o revealing it through a prophet, but He CERTAINLY WILL if He has revealed it]; the Lord will raise him up. If he has sinned, he will be forgiven. 16 Therefore confess your sins to each other and pray for each other so that you may [This interpretation would emphasized the conditionality of this word] be healed.