Our Mishna on Amud Beis rules that a Cohen who performs a sacrificial service without the appropriate priestly investments is considered as if he is a non-Cohen, and the service is invalidated. Gemara Sanhedrin (83b) states, “So long as their priestly investments are upon them, they are considered to be of the priestly caste. If they are not wearing their investments, their priestly status is no longer upon them.”

Indeed the clothing makes the man. This is not only true for Cohanim. Peri Tzaddik (Vayigash 7) compares changing into special garments in honor of the Shabbos to donning the priestly investments. Wearing new and dignified clothing in honor of Shabbos brings upon the person the special Shabbos soul. 

Chaim V’chesed (451.2) speaks of a similar idea, alluded to in Gemara Shabbos (12a): “Ḥananya says: A person is required to feel and check his clothing on Shabbos eve at nightfall to ascertain whether he forgot an object in his pockets that he might come to carry on Shabbos.” Clothing covers the body, in a mystical spiritual symbolic way, Clothing represent the physical body. Just as clothes cover and hold the body, so too the body holds and covers the soul. Hananya is warning that before entering Shabbos make sure the connection between the body and soul is clear, and that you’re not carrying unwanted “baggage“.

Similarly, I once heard a Chassidic interpretation (I can’t remember where I saw it.) In Hebrew, “beged” means clothing, but it shares its root with “boged,” which means betrayal. This teaching suggests that on the verge of Shabbos, one should check their “betrayals,” meaning one should review his actions from the week to ensure he has not wronged anyone. If necessary, he should make amends, entering Shabbos in a state of purity and resolution. In Jungian dream analysis, clothing symbolizes the persona, so it may also imply that one should examine their projected personality traits and qualities to enter Shabbos in an elevated state.