“On that night the king could not sleep.”
It has been pointed out that Esther is unique among the books of the Bible in that it contains no direct reference to God or religion. There are several indirect references to what appears to be divine providence or at least the potential for it, but nothing explicit.
For example, Mordecai tells Esther, “If you keep silent at this time, relief and deliverance will rise for the Jews from another place [Hmm, what place might that be?], but you and your father's house will perish” [I wonder how he could be so sure about that]. Esther responds by telling him to have the Jews fast on her behalf for three days. In scripture, a fast is not a fad diet, but rather an appeal to God.