The Gemara in Menachot discusses at length and over many pages the specific details relating to the laws of tzitzit. At the end of these discussions, the Gemara ends with a braitta which that declares that “all are obligated in the mitzvah of tzitzit: Kohanim, Levites, and Israelites; converts, women and slaves.” (Menachot 43a). Focusing on the first clause, that the mitzvah applies to Kohanim as well as to Israelites, the Gemara asks: Is this not obvious? To which the Gemara responds that I might have thought that tzitzit would only apply to non-Kohanim whose clothes are normally bound by the restrictions of shatnez, and not to Kohanim, since one of their priestly garments, the avnet, the belt, is made out of wool and linen strands – that is, is shatnez. This possibility suggests that tzitzit function as a type of bigdei kehunah for non-Kohanim. For those of us who do not wear bigdei kehunah, we have tzitzit to serve as our religious garments.
The comparison of tzitzit to bigdei kehunah is already made by Tosafot (40b, s.v. Techelet) who discusses a garment which is shatnez because of the addition of tzitzit strings, i.e., when wool strings are placed on a linen garment. Rabbenu Tam says that a person would never transgress shatnez by wearing such a garment even if it was worn at a time when the mitzvah did not apply, like at night. Tosafot states that just as a Kohen does not transgress shatnez when wearing his priestly garments even if he is not doing the Temple service, so a person who wears tzitzit will not transgress shatnez with such a garment. Tzitzit, like bigdei kehuna, are exempt from the restrictions of shatnez. In other words, a garment with tzitzit is a substitute beged kehunah!
Tosafot then goes one step further, and states that even if a Kohen does, in fact, transgress when wearing his shatnez priestly garments this would not be the case regarding tzitzit. As opposed to priestly garments, which have their status only when worn in the Temple and during the service, normal clothes which have tzitzit retain their status whenever they are worn. Such clothes are a type of bigdei kehunah which are more universal than real bigdei kehunah – they are bigdei kehunah that we wear at all times and in all places. These subtle fringes, which are of the very material and color of the garment itself, subtly mark one’s garments as special, and subtly remind a person about his or her function in life and in the larger world.
It is in this way that tzitzit are more powerful than tfillin. Unlike the tfillin, the tzitzit do not have God’s name or Torah verses upon them. Nevertheless, precisely because they are not this holy, they can go anywhere, and can be worn at any time. One can wear tzitzit in a bathroom; one can wear tzitzit on Shabbat; one can wear tzitzit the entire day, even when it is not possible to pay constant or even regular attention to them. They are more powerful than bigdei kehunah which have no function outside of the Temple. Tzitzit, on the other hand, are with us at all times and wherever we go.
The universal nature of tzitzit extends to the people who wear it as well. For while the possibility of women being obligated in tfillin is not given much play in the Gemara, the Gemara (43a-b) seriously considers the possibility that women are obligated in tzitzit, and this is stated specifically in the braitta into which the Gemara reads the implied comparison of tzitzit to bigdei kehunah. Tzitzit are a truly universal garment.
This idea, of framing our activity in the larger world as a taking of the Temple service and the kedusha of the Temple and bringing it to the larger world, was already stated by the Rashba (13th century, Spain) in reference to the hand-washing that we do every morning:
[The reason is] that in the morning a person is created anew… Therefore we have to thank God that God has created us for God’s honor, to serve God, and to bless in God’s name… Therefore, we must also sanctify ourselves with God’s sanctity and wash our hands from a vessel, just like a Kohen who would sanctify his hands from the laver before he would begin his service in the Temple.
Responsa of Rashba 1:191, quoted in Beit Yosef, OH 4
In closing, it is worth noting that in its discussions of tzitzit, the Gemara constantly refers to two special garments – the sadin – the linen tunic, and the tallit she’kulo techelet– the cloak which is fully techelet, sky-blue. What is special about these garments, and why does the Gemara not just refer to the latter garment as a tallit shel techelet, a blue garment. Why does the Gemara always insist that it is kulo techelet, fully blue?
The answer, I believe, is quite obvious. For it is exactly these two garments – the simple tunic worn on the body, and the outer cloak – which directly parallel the two primary bigdei kehunah which the Kohen wears on his entire body. First there is the ketonet, the simple tunic, worn by all Kohanim, which is linen. And then there is the me’il, the outer cloak, which is worn by the Kohen Gadol, and regarding which we are told:
And you shall make the cloak of the ephod, fully techelet. (Shemot 28:31)
The cloak of the Gemara which is fully techelet is none other than the me’il of the Kohen Gadol! It is truly through the wearing of the tzitzit that our clothes become bigdei kehunah, and that we are able to be like Kohanim. Kohanim whose sphere of activity is not limited to the Temple, but Kohanim who wash their hands each morning, prepared to serve God and to bring kedusha in the world.