And he did not many mighty works there because of their unbelief. ~Matthew 13:58 (Mark 6:5)
Why in the world would "unbelief" come into question if God were involved? Isn't an unbeliever exactly who Jesus is talking about in Luke 15:4? (What man of you, having a hundred sheep, if he lose one of them, doth not leave the ninety and nine in the wilderness, and go after that which is lost, until he find it?) If it takes a "mighty work" to "find" the lost sheep, what rational would prevent (Almighty) God from doing so? If only believers are worthy (?) of mighty works, Luke 15:4 is nonsense. Could there be some other explanation?
Among the many jewels in Lissa's talk, her emphasis on "the most essential part is the nurturing care of a health care provider, more so even than the minds positive belief," is noteworthy.
The physicians available in Palestine circa 30 AD were few, and those few were in the employee of royalty (kings and rulers). For 90% (if not more) of the population, doctors weren't an option. Holy men wandering the countryside, "miracle workers," would be (by default) the sole source available for people's relief from physical aliments. This long standing Jewish tradition dates back to Genesis 20:17. (see also; 1 Kings 17:17-24 for Elijah raising the dead) In this context we can find an equitable solution to the inconsistencies referred to above. Jesus fills the role of nurturing health care provider and it helps if the recipient brings a positive mental attitude. Two caveats; 1) placebo's don't always work and 2) even if you know you are receiving a placebo, a cure can be experienced.
So where does this leave us? You are now in possession of some knowledge (if you weren't already) of how the "mechanics" work. If you deem yourself a healer, by all means heal! Just understand the dynamics involved and keep it in perspective. Failure doesn't mean you aren't a healer any more than success says you are. It is the purity of your intent that will answer that question.