C. F. Keil and Franz Delitzsch on Esther 4:3

Est 4:3

Also in every province whither the king’s decree arrived, there arose a great mourning among the Jews. אשׁר מקום is an adverbial accusat. loci in apposition to בּכל־מדינה: in every place to which the word of the king and his decree reached, i.e., arrived. “Sackcloth and ashes were spread for many,” i.e., many sat in hairy garments upon the earth, where ashes had been spread; comp. Isa 58:5. The meaning is: All the Jews broke out into mourning, weeping, and lamentation, while many manifested their grief in the manner above described.