Yes, it's another Reddit "debate religion" question that I felt driven to take on. And here's what I had to say:
I've known people who have been healed of poor vision, breathing troubles, and other ailments from prayer alone. I also know folks just as faithful who have prayed and not been healed.
Here's the thing: God is not some genie, you rub a lamp and get your wishes granted. Prayers are not magic incantations, they are conversations and petitions that may be granted, or not. As Gandalf said of himself, do not take God for a conjurer of tricks. In the Chronicles of Narnia, it was often remarked that Aslan isn't a tame lion, after all.
No one I know who is really practiced in prayer for healing ever promises 100% results. There are people who make that sort of promise, and they are generally hucksters. It's no contradiction to believe that there are both real healers and fraudsters, any more than it is a contradiction to believe that there are both real doctors and snake oil salesmen.
Legitimate churches do not generally preach against medicine or science. The God that gives spiritual gifts is also the same God that gives doctors and nurses their talents and skills. Luke wasn't just the writer of a Gospel, he was also a physician.
Yes, we are to ask God for healing. And yes, we are to seek out the help of trained doctors. And yes, we are to pray that God will bless those doctors and aid their work, even those doctors who may not believe in Him.
So why does God heal some miraculously, others through ordinary medicine, and others not at all? Hard to say. I personally don't think that capriciousness, cruelty, or unfair partiality is in His nature. At least, that's not my experience. My understanding of God's whys and wherefores grows with time, but it's far from perfect.
One priest I heard recently talking on the topic gave this metaphor as food for thought: We are promised that in the final resurrection, all will have healing, of sight, of mind, and of every other ailment. We aren't there yet, and no one can say for sure when it will be. But just a few weeks ago, we had a few days of warm, nice weather, a foretaste of the spring that we know is coming before the cold came back. In the same way, we sometimes get just a taste of Heaven before we get to experience the real thing.