Nicky has recently let rip on the blog about prophecy and cessationism. The question of healing is related, because I think at least one New Testament passage on healing combines that theme with prayer and prophecy.
If you have to, remind yourself of James 5:14,15 and then try and follow my argument.
My thesis is this... Christians can only pray "in faith" for a specific healing if there is a specific promise. Indeed we can only pray "in faith" for anything if there is a promise. In general, we can pray for anything that we think is good... but we should not expect what we request unless there is a promise.
Without checking the relevant experts I think James 5:14,15 is an interesting test case for my thesis. I understand these verses in this way... verse 14 talks about the general pastoral care of all who request such care... verse 15 is talking about prayers for healing offered in faith, that is, prayers offered up upon a supernaturally Spirit revealed promise.
The application of this is that Christian pastors must be very clear with people seeking prayers for healing. Pastors dare not promise what they do not know. Pastors dare not pray certainly for what they do not know. If they do they will soon lose credibility. At the very least they will be very poor pastors.