Gaining a Life Perspective

Why does the Megillah open with "Vayehi bimei Achashverosh," while Al HaNissim in davening begins "Bimei Mordechai V'Esther"? Why the doubled language of "Vayehi" and "hu Achashverosh," and why does the Gemara say we re-accepted the Torah out of love "in the days of Achashverosh" and not in the days of Mordechai? The Vilna Gaon gives one root idea that settles all three. It speaks to anyone who feels that Hashem is hidden right now, and to what Purim teaches us about the stretches of life that look like exile.