The High Priestess traditionally is the guardian of secrets. She is a teacher rather than a doer. But if you listen, you can learn much information you can use.
Followers of the I Ching may know the High Priestess as Yin (passive) to the Magicians Yang (active.) But she is not completely unmoving. Nor is she without power. The Magician works in broad daylight, the High Priestess in the night—preferably on the night of a full moon. The Magician is active. He is working with tools to create power. The High Priestess is more meditative. She too creates power, but with the mind, not using outside tools. She is our INNER thoughts while the Magician is the OUTER action.
In the Rider-Waite deck she sits between two pillars, light and dark, again yin and yang. These pillars are called Boaz and Jachin after the main pillars of the temple of Jerusalem. Boaz means “in strength.” Jachin is the assistant high priest who officiated at the dedication of the temple of Solomon in Jerusalem. Rachel Pollack says “…Boaz stands for passivity and mystery and Jachim symbolizes action and consciousness.” (Pollack, Rachel Seventy Eight Degrees of Wisdom, revised ed. Weiser books, 2007) She sits under a canopy—a chuppa in Judaism, a sacred space.
If you are trying to make a decision and you get the High Priest, the advice is to sleep on it or at least wait a bit. The card says you already have all the information you need, but you may need time to “pull it up.” Time to bring the answer to the front of your mind. So become still, let the stillness talk to you. The answer will come.