Cannabis has many medicinal benefits.
One of the most important things it does, however, is it disrupts the way that your brain makes associations between sensations and memories. Why is this important? Well, you should look in to Cathy O'Brien.
But, for the sake of the explanation, I'll try to be brief: it supposedly ruins or dampens the effects of some "mind control" methods, mostly by doing what was explained above.
Also, this Terence McKenna might also help explain. Many seem to think cannabis isn't a psychedelic, but it is. It might be more so when you consume it in activated forms and not as much when smoking. I could see how that's where the confusion comes from.
As for "killing parasites"โฆ I have no clue. You were on to something with the mention of "something spiritual" though.