God is not explicitly mentioned in the book of Esther. The book, however, in a striking way reveals that testimony to the true God existed in every province of the Persian kingdom of Ahasuerus.
The book begins by mentioning that Ahasuerus reigned “from India even unto Ethiopia, over an hundred, and seven and twenty provinces” (1:1). Beginning with this first occurrence, the word province occurs 29 more times in the book.
Of the 30 occurrences of the word (both in the singular and the plural), explicit statements that pertain to all the provinces in the kingdom in one manner or another occur in six of the ten chapters of the book (cf. 1:1; 2:3; 3:8; 4:3; 8:5; 9:2). This data suggest an emphasis in Esther on matters that were of kingdom-wide importance.
Interestingly, the statement that reveals that there was a kingdom-wide testimony to the true God does not come from the king, Esther, or Mordecai. Instead, it comes strikingly in the middle of the slanderous statement made by Haman to the king:
“And Haman said unto king Ahasuerus, There is a certain people scattered abroad and dispersed among the people in all the provinces of thy kingdom; and their laws are diverse from all people; neither keep they the king’s laws: therefore it is not for the king’s profit to suffer them” (3:8).
Haman testified that a particular group of people (the Jews) were “scattered abroad and dispersed among the people in all the provinces” of the kingdom. We have no reason to doubt the validity of his statement, and the fact that he later authorized letters to be sent to all the provinces to have the Jews in each province be exterminated confirms it (3:12-15).
After stating that these people were present in all the provinces, Haman declared that they were distinct from all the other people of the kingdom because their laws differed from those of everyone else. Saying this, he testified that the Jews were living distinctly from all the others in the kingdom by following their distinctive laws.
The distinctive laws of the Jews, of course, bore abundant testimony to the true God (cf. Exod. 20:1-17). Haman’s testimony, therefore, reveals that there was a kingdom-wide testimony to the true God in the days of Ahasuerus!
 Many later references confirm this understanding that there were such Jews in every province of the kingdom (4:3; 8:5, 13, 17; 9:2; 12-16; 20; 28).