Likutei Sichos – Vol 31 p 170 ff The priorities described in this Sicha explain the behavior of Esther herself, who went to the king after fasting for three days in a row! Page 174-5.

Likutei Sichos Vol 5 pp189 ff The fast of Esther. This class begins with a short and clear discussion of the concept in Chassidus of tzimtzum (G-d “removes Himself” and yet is revealed at the core level). Then Rabbi Paltiel brings to life the situation of Mordechai and Esther after Haman’s evil plot was hatched….