Nothing mysterious here at all. It's unfortunately the age-old story of a charlatan parting the gullible from their money.
This "John of God" is a self-described "medium" and "psychic surgeon." Houdini debunked "mediums" almost a century ago, and James Randi debunked "psychic surgery" decades ago, and even demonstrated how it was done on the Tonight Show:
Yep, I was coming here to post these. James Randi also has a massive cash prize for anyone who can actually prove that they can do this stuff under scientific observation. No one has collected of course.
My first instinct was to say "charlatan" but I see Rich Pell beat me to it. Good to have the video link as proof.
A really good illusionist (aka magician) can create some very compelling appearances of things happening that really are not. And the placebo effect can help folks feel better (even self cure) just by virtue of the body's response to the brain's belief that a something has happened even if it hasn't. The effect is so strong, it needs double blind (neither patient nor doctor knows if the drug being tested is real or a placebo) to try to take that effect out of the test results for a new drug.
The amount of marketing and promotion on the website linked to also adds to my conviction of charlatanism. The (assuming you belive in them) real miracle workers of history - saints and the like - invariably have downplayed their abilities not marketed them and when they were sought after due to word-of-mouth reputation they did their healing for free.
There is truly more in Heaven and Earth than dreamt of in science (Shakespeare, I'm told, was referring to the Horatio's university studies in "Natural Philosophy" which is what they called science in those days.) and there are many things science may never explain, but this healing, I think, is illusion and not reality.