Absence of Explicit References to God in Esther

From the Concordia Self-Study Bible introduction to Esther:

An outstanding feature of this book--one that has given rise to considerable discussion--is the complete absence of any explicit reference to God, worship, prayer, or sacrifice. This "secularity" has produced many detractors who have judged the book to be of little religious value. However, it appears that the author has deliberately refrained from mentioning God or any religious activity as a literary device to heighten the fact that it is God who controls and directs all the seemingly insignificant coincidences that make up the plot and issue in deliverance for the Jews. God's sovereign rule is assumed at every point, an assumption made all the more effective by the total absence of reference to him.