According to R’ Dovid Feinstein, the word for “ready” as written (atudim) with a vuv implies permanence, in a state of remaining. In other words, the Jews should remain ready for future events. He quotes the Talmud (Shabbos 88a) about the Jews being miraculously coerced by H-Shem into accepting the Torah at Sinai under a threat of annihilation. In contrast, the Jews re-accepted the Torah at the end of Megillas Esther (Esther 9:27) under no such threatening pressure, and under not such obvious miracles.
Ginzei HaMelech writes that this could also be an allusion to the continuing future battle of the Jewish people against Amalek. He quotes the words of the Rambam (Mishneh Torah, Hilchos Megillah 2:18) that all of the works of TaNaCh will no longer be needed once Moshiach comes. The exception to this is Megillas Esther. The Ginzei HaMelech explains that the war against Amalek mentioned in the Purim story will still be relevant after Moshiach. It is a day for which the Jews should continually be prepared.
The Talmud (Megillah 12a) informs us that Haman and Achashverosh made the party for the express purpose of causing immorality there. If Jews sin through coercion, they are not held liable in the Heavenly court. On the other hand, if they (Heaven forfend) succumb without force, they become fully responsible for their actions.
The Malbim adds that, since there were so many cups at the feast, everybody had their own, and did not have to share. As such, no guests were forced to hurry with their drinks.
The Ohr HaChaim, in his Rishon L’Tzion adds that Achashverosh put the most delicious non-kosher cuisine before the Jews, hoping they will sin on their own. His ultimate goal would have been to strengthen his kingdom by restraining the Jews from rebuilding their own.