Shekalim, Chapter Eight, Mishnah Four
This mishnah discusses the impurity of the curtain which separated the Holy of Holies from the remainder of the Temple.
1) If the curtain [separating the Holy of Holies from the rest of the Temple] was defiled by a derived uncleanness, they immerse it within [the precincts of the Temple] and they bring it back in again.
2) But if it was defiled by a principal uncleanness, they immerse it outside and spread out in the Hel.
a) If it was new it was spread out on the roof of the colonnade, so that the people might behold its workmanship which is beautiful.
Section one: This section discusses a case where the curtain (parochet) was made unclean by a derived uncleanness. This term refers to something that has become unclean by virtue of its contact with something that is a principal uncleanness. From the Torah (deoraita), only liquids which come into contact with derived uncleanness are made unclean. Derived uncleannesses do not cause things or people to become unclean. Therefore, the curtain in this case has been made impure with only a low level of impurity, one that is considered to be derabbananof rabbinic origin. The rabbis nevertheless required that it be immersed but they allowed it to be immersed in the mikveh (ritual pool) that was in the precincts of the Temple. Furthermore, it could be brought back again immediately. If it had contracted deoraitatoraitic impurity, it could not be used again until nightfall, as we shall see in the next clause.
Section two: If it came into contact with a principal uncleanness, for instance a zav or zavah (people with unusual genital discharge), or with a sheretz (a creeping animal) then it must be taken out of the Temple to be immersed. There in an area known as the Hel, which was inside the gates of the outer walls but outside the Ezrat Nashim (the womens courtyard) it is let out to dry.
If the curtain was knew, they would spread it out in a place where people could see it from far off for it was very beautiful. In its normal place, right in front of the Holy of Holies, few people would have the chance to see this magnificent work.