She sits at the gate before the great Mystery, as indicated by the Tree of Life in the background.
The moon under her left foot shows her dominion over pure intuition. The palm indicates fertility of the mind and the cube on which she sits is the earth. The planet associated with the High Priestess is the Moon.
She represents spiritual enlightenment and inner illumination, divine knowledge and wisdom. She generally appears in a Tarot reading when you need to listen to and trust your inner voice.
The High Priestess in a Tarot reading can also point to the unknown and can indicate that your life is changing.