In Ma’aseh Chemed, the Steipler Gaon writes that the letters do not explicitly name the Jews’ enemies in contrast to Haman’s letter (Esther 3:13). There, Haman was concerned that some people might misinterpret his decree to target some other disliked minority. Therefore, he spelled out clearly who the enemies were. By being specific, the ring-leaders could start making plans, stockpiling weapons, collecting Jewish addresses, etc. However, by performing these acts, the Jews’ enemies made themselves conspicuous to the Jews. For this reason, the purported enemies in this verse could be vague because Jews knew exactly who they were already. How complete and precise is H-Shem’s justice! Haman and his cohorts dug their own graves.
Rav Dovid Feinstein writes the king should be expected to ask advice before proclaiming a major ruling. In a case like this, though, he also needed a sense of what was best – not just what was right. This required both knowledge and justice. The Midrash (Esther Rabbah 4:1) points out that Achashverosh, though not a righteous man by any stretch of the imagination, still had a “mida tova” (good characteristic) of seeking advice before making big decisions. Rabbi Eliezer Ginzburg writes in Ginzei Hamelech that “justice” implies going beyond the letter of the law.