Having experience with numerous (in the high 30s) drugs and psychoactive plants I can say that I don't think the Cannabis/"Marijuana" plant comes anything close to those sorts of religious experiences people associate with the "third eye".

I have had such experiences, including ego death/Buddhist nirvana and similar experiences of transcendence under the influence of Psychedelics (5HT2A agonist hallucinogens, e.g. LSD, Psilocybin Mushrooms, Ayahuasca, Mescaline. Don't get these confused with other hallucinogens like dissociatives e.g. Ketamine, PCP etc, or Deliriants, e.g. Datura, Diphenhydramine.) and also while sober and practising meditation and yoga.

I have not had anything remotely similar though under the influence of Cannabis and find it actually makes these sorts of states a lot harder to reach.

For me Cannabis has the following benefits:
- Good for thinking about one's own life and how to improve it
- Improves creativity
- Stimulates appetite
- A great social drug with far fewer negative side-effects than others such as caffeine or alcohol

It isn't some spiritual wonder drug though, and for that area you're better off looking at psychedelic plants like Psilocybin Mushrooms and the Ayahuasca brew

Also, be careful with Cannabis, as smoking it regularly in large amounts interferes with dreaming, something I'm sure no-one on this site would want! (on a side-note, sub-threshold doses of deliriants that do not produce any noticeable effects will give lasting dream recall and enhancement for as much as a week after a single dose)