If clothes do not make the man they certainly influence the man. A policeman who dons his uniform consciously or not is donning upon himself not only specific and unique garments that identify his profession, but responsibility and commitment to others. This is one of the many items on the long list of "we had it first" ideas that the Torah teaches. The Kohanim in the Beis Hamikdash, we are taught in Parshas Tetzaveh, wore special garments, "l'chavod u'l'sifares - for honor and splendor" (Shemos 28:2). At first glance this is to be understood as honor for the One they served, and honor for the House in which they served. Indeed, this is the way the Sefer HaChinuch (99) understands this mitzvah. I'd like to suggest however, that in addition these special garments, unique to the Kohanim, brought out their honor and splendor.
The Ibn Ezra in his interpretation of the l'chavod u'l'sifares notes, "sheyisparau bahem - that their honor may be revealed through them." Rashi famously comments regarding Aharon's lighting of the menorah, (Bamidbar 8:3) "melamed shelo shina - this teaches us that he did not deviate." The Sfas Emes z"tl understands this to mean he did not deviate from his initial excitement and commitment; the privilege of lighting the menorah never became a routine matter. Perhaps his donning of the priestly garments which, as the Ramban notes, reflected royalty, assisted him in maintaining his incredible focus. Indeed, Reb Yochanan referred to his garments as, "m'chabdusai -that which honors me" (Shabbos 113a.)
Clothing plays a most important role in the Sanctuary, as we are taught, "while clad in Priestly garments their Kehuna responsibilities and effectiveness as officiating is valid" (Zevachim 17b); without the exact prescribed attire of the Kohen, they are no better than a zar (a non-Kohen) and their service would be invalidated.
An additional appreciation of clothing may be learned from the laws of Shabbos and Yom Tov attire. The Talmud (Shabbos 113a) teaches that one's garments for Shabbos should be better and different than those worn during the week, and if possible one's attire for Yom Tov should be even of a better class. A possible reason for this was explained by the Rav z"tl, that on Shabbos Hashem comes to visit us and we dress accordingly. On Yom Tov when we go to visit Him, if possible we upgrade the clothes to mark the specialty of the occasion. Here too our donning Shabbos and Yom Tov clothing brings out a greater respect and appreciation for Shabbos, and in turn elevates our persona on these holy days.
It is interesting to note that regarding the forthcoming holiday of Purim there is an old custom to masquerade in costumes and conceal our true identity. The B'nei Yissaschar in Ma'amarei Chodesh Adar (9) suggests the following explanation for the custom: the Gemara (Megillah 12a) teaches that the Jews were guilty of bowing down to the statue of Nevuchadnetzar, but they only sinned on the surface. That is to say, they feigned serving the idol, while in their hearts they remained loyal to Hashem. Hashem acted midah k'neged midah and therefore feigned a threat to (G-d forbid) destroy the Jewish nation in order to scare and arouse the Jewish nation to teshuva; there never was a Divine plot to destroy His people. We therefore masquerade at the time of the Purim Seudah, thus demonstrating and proclaiming the message that we need to learn from, and rectify, the past. They failed to have their inner resolve prevail over their actions; their penimius did not influence their chitzonius.
Purim was a day of v'nahafoch hu - topsy-turvy, and what appears on the surface was not genuine. The Talmud (Megillah 12a) teaches that King Achashveirosh, to celebrate that the Jews would not be rebuilding their Temple nor returning to their land, clad himself in the bigdei Kehuna to defiantly mock the Jews by saying they would no longer be needing these garments.
The Jew relives his past, he does not only remember it. It is not enough to recall that those who left Egypt ate matzah, rather we also eat matzah. We remain awake all night on Shavuos, anxiously awaiting our receiving the Torah. We reside in Sukkos. It is thus most appropriate that we masquerade on Purim, laughing at and mocking the outer trappings and behavior of the another individual, and thereby reminding ourselves that the penimius, i.e. the inner core, commitment, and image of G-d and true character is what saved the Jewish nation at Purim, and reminding us that this is to be our true perspective and identity all year long.