Theresa of Avila, one of the most popular saints of the Catholic Reformation, wrote narratives of her mystical experiences aimed at the nuns of her Carmelite Order; these writings had become popular reading among lay people interested in pursuing spirituality.
Theresa's face reflects not the anticipation of ecstasy, but her current fulfillment, which can only be described as orgasmic.
Theresa described her bodily reaction to spiritual enlightenment in a language of ecstasy used by many mystics, and Bernini did her the favor of taking her seriously.