The Malbim writes that Achashverosh emphasizes that Haman should do this, himself because Mordechai deserves these, and Haman does not. Therefore, as either a punishment or an opportunity to take part in honoring the king, he should get these items instead of asking servants as Haman (Esther 6:8-9) suggested.
Additionally, Me’am Loez points out that Haman is the trusted adviser of Achashverosh, so the king would prefer Haman handle the king’s precious items, and not servants with their grubby hands.
Perhaps Achashverosh, being the evil man he is, wants to lessen the reward given Mordechai by cutting out the honor implied by the presence of many servants.
Class Participant YML, however, pointed out that Haman represents the king, the source of this honor, more than do the servants. By Haman serving Mordechai directly, this would exponentially boost the honor Mordechai is receiving.
The Alshich writes that, in his desire to uncover the conspiracy he so fears, Achashverosh is emphatic that Haman should perform everything he suggested.
The Me’am Loez explains that the nature of a person who is forced to do something is to delay and ignore as many steps as possible.
According to the Talmud (Megillah 16a), once Haman saw that he would have to honor Mordechai in this degrading way, he suggested new methods of honoring him that would not detract from his own self-love, like naming a river or village after Mordechai. In an ironic twist, Achashverosh therefore stresses that Haman should follow every detail to include those other things Haman suggested, as well.
The Shaar Bas Rabbim writes that this phrase includes the crown. Although Achashverosh is not happy with the idea, even showing his disapproval, he nevertheless agrees to it reluctantly, not even able to say the word.
The Ben Ish Chai writes that H-Shem wanted Mordechai to be pampered with all of these honors for two reasons. First, on the Earthly level, Mordechai deserves reward for having saved the life of Achashverosh, allowing him to be pampered in palace luxury. Second, on the Heavenly plane, the Talmud (Gittin 62a) refers to scholars as royalty, deserving of the best in this life and the next.
In the spirit of the idea that the entire Purim story teaches us that H-Shem runs His world through mida kineged mida, M’nos HaLevi explains that when Mordechai first learned of the decree to annihilate the Jews, he is described (Esther 4:1) as putting on sackcloth, walking through the streets of Shushan, and crying bitterly. In reward for putting on the sackcloth, he is now to put on royal garments; in reward for walking through the streets, he is now to be escorted on the king’s horse; and in reward for his bitter cry, his greatness is to be proclaimed throughout the city.
R’ Moshe Dovid Valle points out that the initial letters of the last three words in this verse “mikol asher dibarta” (“from all that you said”) spell out the word m’od (“much”). The Torah (Bireishis 15:1) describes Avraham’s – and by extension, every righteous person’s – reward as s’charcha harbeh m’od, “your reward will be very great.”
R’ Chaim Fasman once pointed out that the only part of the daily amida in which we request that somebody actually get something is in the prayer for the righteous, where we ask H-Shem that He give the righteous s’char, reward. The reason for this is that it is an inspirational kiddush H-Shem for all of us when we see the righteous rewarded.
The Targum Sheini, with its embedded commentary, says that Achashverosh told Haman a detailed list of the items which he was supposed to give to Mordechai, including Achashverosh’s Macedonian crown, Ethiopian sword, African cloak, and the horse he rode from the beginning of his reign named Shifrigaz. The gematria of Shifrigaz (300+10+80+200+3+7=600) is 600, the same as sheker (300+100+200=600), falsehood. Perhaps this alludes to the idea that wealth and honor are fleeting, impermanent things, as the verse in Koheles (6:2) says, “a man to whom G-d has given […] wealth and honor […] and yet G-d has not given him the opportunity to eat from it, […] this is futile and an evil disease.”
The Yad HaMelech points out that Achashverosh stresses that Mordechai sits at the king’s gate in order to allay Haman’s concern that honoring Mordechai may be beneath his dignity. This is not to imply that Achashverosh suddenly cares about Haman’s honor; in fact, if Haman were to honor somebody lowly, that could reflect poorly on Achashverosh, his king.
According to the Talmud (Megillah 16a), Haman attempted to stall by pretending to not know which Mordechai Achashverosh had in mind, and the king had to narrow down the identity of this particular Mordechai.
The Maharal says that the reason Haman’s advice of giving the honoree the crown (Esther 6:8) is not mentioned again is because the king should ordinarily give these items, himself. However, in the case of this person who is a major adviser who “sits at the gate of the king,” Haman can bring him the crown.
The Ginzei HaMelech notes that Achashverosh here does not describe Mordechai as one “who sits at my gate,” but rather the “gate of the king” because he is alluding to the fact that Mordechai sits at the gate of the King, H-Shem. Earlier (Esther 2:5), when Mordechai was referred to as the “son of Kish,” the Talmud (Megillah 12b-13a) understood that to mean that he knocked (“hikish”) at the Gates of Mercy. His praying therefore qualified him to be called one who sits at the gate of the King.
According to the Alshich, there is an implied conversation between Haman and Achashverosh here. After Achashverosh tells Haman to honor Mordechai, Haman responds that Achashverosh should not desire to honor a Jew since Haman had acquired all of the Jews (see Esther 3:11), including Mordechai, to which Achashverosh responds that Mordechai is different since he “sits at the gate” – he is an adviser to the king, so he can be honored.
Answering this question, as well as the next, the Me’am Loez writes that Haman was implying that Mordechai was one to whom Achashverosh owes a debt – and no more.