Herodotus tells us that Persians “are extremely fond of wine;” indeed, “it is usual for them to be drunk,” particularly “when they are debating the most important issues.” They attach so much importance to inebriation that “any issues they debate when sober are reconsidered by them when they are drunk.”
Herodotus Histories, I, 133, p. 61. It is now clear why Esther had to arrange two separate drinking parties. Since she obtained permission from the king to invite Haman when the king was not inebriated (see Est. 5:4), it was not official. Therefore she organized the first party in order to receive permission from the king to invite Haman when the king was inebriated (see Est. 5:7-8). Once official permission was obtained, she organized a second drinking party to present accusation against Haman (see Est. 7:2-5). This is why, although the king had granted Haman permission to kill the Jews (see Est. 3:8-11), he was furious  when he learned that Haman wanted to proceed with his plan (see Est. 7:5-7), although permission was granted when he was sober. It is worth noting that the Shiites in Iran reject the tradition ascertaining that Mohamed had forbidden to drink wine.
 The Malbim has a different explanation I cited it here.