Psilocybin is fundamentally mediated at 5-HT2A receptor sites, and effects can include strong changes in perception, cognition, affect, volition (using ones own will), and somesthesia (the faculty of bodily perception).  The 5-HT2A receptor was first noted for its importance as a target of serotonergic psychedelic drugs such as LSD.In a study conducted at Johns Hopkins University, psilocybin produced extreme anxiety/fear in 39% of volunteers and/or mystical experience in 72% of volunteers.  Is it possible then that mystical experiences are linked with altered states of perception and would that be seen as a threat from major religious institutions?
Psilocybin has been used in cultures for divinatory or religious purposes but in early clinical research, experiences varied from negative to positive and prominent mystical experiences were rare. Griffiths et al notes that this had a lot to do with primitive techniques used in the research studies but now higher doses have a greater amount of preparation and interpersonal support.  As a result, higher rate of positive experiences, and mystical ones were reported. A month after the high dose sessions, psilocybin experience was rated as having substantial personal and spiritual significance, and sustained positive changes in attitudes, mood, and behavior in majority of the volunteers and at 14 months, the positive changes were not diminished. 
The verbatim from the volunteers are inspirational and telling. Horrible experiences are an illusion and universal love lies beneath it all. To go beyond the ego is to let go without anxiety and without direction. Time and space collapses and one is engulfed in the unification of existence and consciousness. One gets the sense that everything is one and our only purpose is to receive love. We become points awareness with no reference to time and space where we uncomfortably experience death, but then are in absolute peace as we become engulfed in the presence of unconditional and universal love.
These mystical experiences are considered by volunteers to be among the most life changing and spiritual experiences of their lives and produces positive changes in attitudes, mood, altruism, behaviour and life satisfaction. The study noted that "In addition to possible therapeutic applications, the ability to potentially produce mystical-type experiences should permit rigorous scientific investigations about their causes and consequences, and mayprovide novel information about the biological bases of moral and religious behaviour." 
Psilocybin occasioned mystical-type experiences: immediate and persisting dose-related effects.