Significance: As a well esteemed Enchanter of the Circle, Vivienne becomes the Grand Enchanter; she is very powerful, yet very disciplined. A High Priestess is basically what she is.
The card itself represents: Trust in our own intuition, looking deeper, thus insight, seeing behind the façade, secrets revealed, hidden truths and hidden destiniy revealed, cleansing, spiritual developments, dreams and visions, etc.
Being in Orlais for a time, she can see behind the masks of the Orlesians, their façade, and trusts greatly in her own powers.
Reversed: Fatigue, clouded insight, vanity, laziness, loss of motivation, discretion that is required, short-sightedness, the inability to recognise intuition and therefore ignoring intuition, etc.
Dressed in a long flowing gown, she stands confidently; her staff transforming into an upside down black snake, the symbol of the life force and primal energy, as a spirit guide, and Vivienne is a healer, therefore healing and transformation. A circle in a square, a symbol of heaven and earth, floats near her face; two lines dropping down to meet the circle form an arrow; the power of spirits come down to her aid. She holds a white chalice, its stand becoming one of the many symbols of the Divine Feminine. The colour black represents power, elegance, and yet death and evil; however, a bright light shines on her face, casting aside all shadow of doubt. The face and torso of a masked man in the background, depicts her Orlesian lover who is ill. Associated with the moon, the High Priestess represents the magical prowess that Vivienne so gracefully embodies.
What I think this means for Vivienne: Light will always be cast where there is doubt, and she will leave her past in the shadows and bring clarity to the Circle and make great changes as Grand Enchanter.
What I think this means for DA: The Circle of Magi will be completely reshaped, its darker traditions will be cast aside, and new enlightenment about Mages will be brought to Thedas.
Links to the Tarot Decks Used in the Comparison, the DAI Tarot Deck, and the Books used to determine what the cards actually represent: