When I look at the Rider deck version of this card I see a man dressed regally in the vestments of the Pope sitting on his throne between two pillars. His right hand is lifted, with two fingers raised to form a sign of the benediction. To the left and right here are two acolytes (a.k.a. initiates) before him preparing to take up their appointed roles.
This looks like a formal church setting to me. Between them at the feet of the Pope are two crossed keys at the bottom of the card. What do the keys unlock? The gates of heaven and hell?
So to me there is a rather uneasy relationship with religious tradition. Especially the pope-like hierarchy, or the structured system that requires adherence.
But mainly I see in the symbols the need to conform to rules via a common belief.
Three words come to mind when I look at this card:
1. belief
2. conforming
3. identification
I have a sense of identification with structured groups (the group identity) with rules, procedures, and ritual. Remember in addition to the churches, there are schools, clubs, teams, companies, bowling leagues, internet forums <g>. For me the card can stand for any institution, their values and the roles assigned to membership.
Therefore in my readings, having the Hierophant/Pope/High Priest appear in a reading may have some provoking implications. He points the way to the possibility of a struggle with this institution or group that does not regard your innovative, free-spirited or individual effort. These groups can be elevating or oppressive, depending on circumstances and position of the card along with the surrounding indicators. Sometimes we need to follow the program (i.e. embrace tradition). At other times we need to trust ourselves and break with convention.
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Gilabno: Greater Secrets
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A short side note:
As someone has already mentioned the Hierophant was the High Priest at the Temple in Eleusis, near Athens. A celebration held annually in honor of Demeter and Persephone called the Eleusinian Mysteries was presided over by the Hierophant. These rites were the most sacred and revered of all the ritual celebrations of ancient Greece. As Christianity began to spread, the Mysteries were condemned by the early Church fathers and eventually subsumed by the church rituals. There are a lot of good resources about this on the internet just search on Eleusinian Mysteries.