One Sheep, 70 Wolves, and a Great Shepherd
The Gemara  explains that one of the reasons the Jewish people were threatened with annihilation - Heaven forfend - during the time of the Purim story was because "they derived pleasure from the banquet of that evil person [King Achashveirosh]."
The text indicates that it was not because of our attendance at the banquet - which was mandatory,  and moreover the food and drink served was kosher  - that the harsh decree came about. Rather it was because we "derived pleasure."
What was it about deriving pleasure from this banquet that was so appalling that it nearly resulted in the destruction not only of those who attended, but even of those who were not invited?
Our Sages  liken the existence of the Jewish people in times of exile to a "solitary sheep that finds itself surrounded by 70 wolves." Thus, "great is the Shepherd who protects and guards His flock." Consequently, the continued existence of the Jewish people is sometimes dependent upon miraculous means - the watchful eye of the "Great Shepherd."
The Jewish people are assured of G-d's protection only when our conduct is consonant with relying on Him for protection. However, when we choose to rely entirely on natural means - on one or more of the "70 wolves" - then we remove themselves from His divine protection  and place ourselves at the mercy of natural forces.
The reason our "pleasure" was the cause of such a terrible decree will be understood accordingly: It was not punishment for a sin, but rather the natural consequence of our conduct.
After the king had elevated the evil and anti-Semitic Haman to a position of exceptional power, the situation of the Jewish people was similar to that of the "solitary sheep that finds itself surrounded by 70 wolves." At the same time, our conduct - "deriving pleasure..." - forfeited miraculous protection.
For this invitation to the feast was so important to the Jews of that time, they were so extremely honored by the invitation, that it caused them a great deal of pleasure. Thus they partook not because they had no choice, but because of their delight in being invited.
Since the Jewish people themselves gave credence to one of the "70 wolves" and took pleasure in being invited by "that evil person," they annulled their supernatural guardianship. Instead, they placed themselves at the (natural) mercy of the "70 wolves" - something that threatened the continued existence of the solitary sheep.
It is true that while the Jews are under the dominion of another nation they are obligated to honor that nation,  obey its laws,  and pray for that country's peace and welfare.  Thus, when King Achashveirosh invited the Jews to attend the feast, they were compelled to do so.
Nevertheless, they should have understood that the existence of the Jewish people is not at all contingent on any king of flesh and blood, but wholly dependent on G-d. Moreover, the ongoing existence of the Jews is a miracle clothed in the garments of nature - "great is the Shepherd" who guards us in a manner that transcends the world.
Thus, their pleasure that so important an evil person as King Achashveirosh - upon whom they felt their lives depended - invited them to a meal, indicated that they had forsaken their trust in G-d and had placed their faith in the hands of one of the "wolves."
This also helps us understand why Purim is unique among all the Festivals that celebrate G-d's miracles on our behalf, in that it commemorates a miracle that was completely clothed in nature. 
The reason for this is as explained. Since the evil decree came about because the Jewish people chose to rely totally on the forces of nature, the Purim miracle therefore revealed, within nature, that G-d's conduct with the Jews - even as they exist in the natural realm - is truly above and beyond the natural.
Based on Likkutei Sichos, Vol. XXXI, pp. 170-174.
- (Back to text) Back to text Megillah 12a. See also Shir HaShirim Rabbah 7:8.
- (Back to text) Back to text Esther Rabbah 7:18.
- (Back to text) Back to text Megillah, ibid.; Esther Rabbah 2:13.
- (Back to text) Back to text Tanchuma, Toldos 5; Esther Rabbah 10:11.
- (Back to text) Back to text See Berachos 29a.
- (Back to text) Back to text See Rashi, Vayechi 48:2, Shmos 5:3, 6:13, 11:8.
- (Back to text) Back to text Nedarim 28a; Rambam, Hilchos Gezeilah VeAveidah 5:11ff.
- (Back to text) Back to text See Yirmeyahu 29:7; Avos 3:2.
- (Back to text) Back to text See Torah Or, Megillas Esther, p. 93c ff., 100a ff. See also Likkutei Sichos, XVII, p. 154 fn. 51.