The Talmud (Megillah 13b) and the Midrash (Esther Rabbah 7:12) both interpret “yeshno” (“there is”) as rooted in the Hebrew “yashan,” (“sleep”). According to the Talmud, Haman was maligning the Jews to Achashverosh by claiming their sleeping, or spiritual lethargy in performing the mitzvos that the king otherwise feared would protect them.
The Midrash there, likewise, interprets this word as a means for Haman to allay the fears of the rightfully nervous king by claiming that H-Shem, Himself was sleeping, or not concerned about the goings-on in the world. In the Midrash, H-Shem responds by quoting Tehillim (121:4) that “the Guardian of Israel neither sleeps nor slumbers.”
In Ohr Gedalyahu, Rav Gedalya Schorr cites Nefesh HaChaim that these two opinions are not necessarily contradictory, for when the Jews act toward H-Shem with indifference, mida kineged mida (measure for measure), H-Shem will look upon them with indifference, as well.
The Sfas Emes writes that the reason Haman thought that H-Shem was “sleeping” was because the Jewish people were too focused on their “yesh” (“there is”), their possessions, the physical. The more the Jews focus on yesh (the physical), the more they will be yeshno (spiritually sleeping). As the Ohr Gedalyahu puts it, Jews are sleeping when they perform mitzvos without care. This is often a consequence of thinking that abandoning Jewish observance will cause the gentiles around us to behavior towards us in a a more favorable fashion. On the contrary, Rav Hirsch (Collected Writings, Volume II, 366) writes that it is a “self-deception for us to imagine that we could buy the friendship of the peoples and permanently assure it to ourselves by discarding this Jewish distinctiveness.”
The Torah Ohr points out from the Talmud (Baba Basra 16a) that the Yetzer HaRah (Evil Inclination) is the Satan (Heavenly Accuser), and that is the Angel of Death. What this means is that the very thing in our lives that seduces us to sin is also our judge and executioner. Haman acts the very same way; Haman is the seducer in setting up the feast where they Jews sinned, Haman is the judge who decided the Jews deserve death, and he wishes to be the one who does the actual killing. Certainly, being seduced by the Evil Inclination is not an excuse for misbehavior. On the contrary, H-Shem gives us all precisely the very tools – whether psychological, spiritual, physical, or otherwise – needed to successfully combat the exact temptations we experience (Nesivos Olam).