The worship itself was entrusted to the kohanim, who had to prepare themselves for their task and to be clothed in special garments. So important were the priestly garments that the Torah says, “They shall be upon Aaron and his sons… that they bear not iniquity and die” (Ex. 28:43).
Rashi sums up the view of the rabbis when he says that a kohen who officiates without his official vestments renders himself liable to death at the hand of God.
The vestments served two purposes – kavod (honour) and tiferet (glory) (Ex. 28:2), the honour of God and the glory (i.e. dignity) of the kohen. They were not merely clothing to keep the kohen’s body warm, covered and protected, but to endow his rank with self-respect and respect on the part of the people.
Nachmanides compares priestly vestments with royal robes: just as a king wears robes to symbolise temporal office, so too a kohen has special attire as a mark of spiritual authority.
Later on in many communities it became customary for rabbis and cantors to wear special robes (in England called “canonicals“). It was argued that this derived from the priestly vestments laid down in the Bible, but this assertion is quite suspect as a matter of history.
Firstly, the priestly service was regarded as invalid without the wearing of vestments, and no-one can argue that a synagogue service is halachically ineffective unless the officiants wear special robes (an attempt at making robes into an indispensable requisite was made in the by-laws of the United Synagogue in London, but this was never argued on halachic grounds).
Secondly, Jewish worship does not require an ecclesiastical caste and in theory any layman can officiate at any service (except for duchaning, which must be carried out by kohanim).
The fact that a style of synagogue costume developed for rabbis and chazanim in order to lend added dignity to the service derives more from social mores than from Jewish law. In some countries social mores also influenced the street dress of Jewish clergy, and certain features, such as the clerical collar that was once widespread in British countries, came directly from Christian usage and have now been entirely abandoned.
From the point of view of Jewish law, the really important requirements for rabbinic dress are, as codified by Maimonides, that “The dress of a wise man should be suitable and clean… It is forbidden that stains or grease-marks should be found on his garment. He should not wear the apparel of princes, e.g. garments of gold and purple, to attract the attention of people, nor the clothes of paupers which bring disrespect on the wearer; but his garments should be of a medium character and suitable for him.
“His flesh should not be visible through his apparel, nor should his dress drag along the ground. He should not wear his tallit conspicuously long because it appears like haughtiness, except on the Sabbath if he has no other in its place. He should not wear patched shoes in summer, but if he is a poor man he may wear them in winter. He should not go out into the street perfumed, nor with scented garments… All these rules are intended to avoid suspicion” (Hilchot De’ot, chapter 5).