There is a chiyuv [obligation] to have a haircut before Yom Tov, what is behind this?
The Shu”t Binyan Shlomah (siman 10, d.h. venireh) offers a novel insight into what is behind this: When the Beis HaMikdosh was standing, there was an obligation to come and see the azorah, the obligation known as re’iyas pnei azorah.
The Rambam (Hilchos Bi’as Mikdosh 1:17) writes: “It’s forbidden, for a Yisroel or a Kohen to enter the Beis HaMikdosh from the Ezras Yisroel and inwards, after drinking wine, or whilst drunk, or with messy hair (פרוע ראש דרך נוול) or with torn clothing.” We see from the Rambam, that one isn’t allowed to enter the Beis HaMikdosh with messy hair. In order to ensure that no one missed out on the mitzvas aseh of re’iyas pnei azorah, and to ensure no one violates the prohibition of מקדשי תיראו – fearing the Beis HaMikdosh, Chazal enacted that people should have haircuts before Yom Tov.
With this we can understand why Chazal said that there is a chiyuv to have a haircut before Yom Tov, כדי שלא יכנס לרג ל כשהוא מנוול – “in order not to enter into Yom Tov looking unkept”. Surely, they should have said it in a positive manner and said, כדי שיכנס לרגל דרך יופי וכבוד – “to ensure one enters into Yom Tov in an honourable manner”, why do they focus on the negative? Based on the above, however, that the main reason is so that we one doesn’t end up entering the azorah unkept and violating מקדשי תיראו, we can understand why it was said in this manner.
The question is, we no longer have the Beis HaMikdosh so why is there still a chiyuv to have a haircut before Yom Tov nowadays? The answer is, once such a takonah was made, Chazal kept it in place, because מהרה יבנה בהמ״ ק – “we hope that the Beis HaMikdosh will be speedily rebuilt”.
The Shu”t Siach Yitzchok (R’ Yitzchok Weiss, 243:14) suggests a different reason for why the chiyuv remains today. The Shu”t Sho’el U’meishiv (Mahdura Telisoh 123) explains that the reason we tovel [immerse in a mikveh] nowadays before Yom Tov even though we have no Beis HaMikdosh, is because of zecher leMikdosh [to remember what was done when we had the Beis HaMikdosh]. The Siach Yiztchok suggests that we can say the same thing with haircuts (we find this idea in the Gemara in Menachos 66b which says, the mitzvah of sefiras ha’omer is derabonon because of zecher leMikdosh).
