The High Priestess represents female energy, secret knowledge, mystery, particularly the mysteries that women hold in their hearts. Of the High Priestess, Aeclectic Tarot says:

If there is a card that symbolizes the tarot reader is it the High Priestess. A woman (or man!) of psychic powers, intuition and secret knowledge. Where the Magician is about revealing, the High Priestess is about keeping things hidden behind the curtain. Things you know, but don't tell.

If the reader feels the High Priestess stands for the Querent, then this is a time of solitary investagation and the passing on of secret knowledge. The Querent might find themselves spending time in old libraries, reading through dusty documents and letters, or studying old religious texts. Things kept secret will be revealed to them. Likewise, these secrets might come to them psychically by way of visions or powerful instincts. Insights may be found in crystal balls, tea leaves, dreams or conversations with spirits.

LearnTarot.com says that the High Priestess is a card of waiting, of stillness, and:

In readings, the High Priestess poses a challenge to you to go deeper - to look beyond the obvious, surface situation to what is hidden and obscure. She also asks you to recall the vastness of your potential and to remember the unlimited possibilities you hold within yourself. The High Priestess can represent a time of waiting and allowing. It is not always necessary to act to achieve your goals. Sometimes they can be realized through a stillness that gives desire a chance to flower within the fullness of time.