After the Torah in Parashat Naso commands that Teme’im – people with Tum’a (impurity) – must be distanced from the site of the Mikdash, it then warns, “Ve’lo Yitam’u Et Mahanehem” – “They shall not defile their camp” (Bamidbar 5:3). The Gemara in Masechet Makkot (14) explains this phrase as introducing a separate command – a prohibition forbidding somebody who is Tameh (impure) from entering the site of the Temple. In addition to an affirmative command that such a person must avoid the site of the Temple, the Torah also establishes a prohibition against entering the site in a state of Tum’a (impurity).
The Sefer Ha’hinuch writes that this command applies to anyone in a state of Tum’a that requires immersion in a Mikveh on the level of Torah law, or a person who came in contact with a human corpse and thus requires sprinkling with the purifying waters of the Para Aduma. It also applies to somebody who immersed in a Mikveh but remains impure until sundown (a state known as “Tebul Yom”); he may not enter the site of the Temple before sundown. If anyone in one of these states of impurity enters the site of the Bet Ha’mikdash, he has transgressed this prohibition, and is liable to the grave prohibition of Karet.
The Sefer Ha’hinuch explains that there are some forms of Tum’a which are not included in this prohibition, and a person with one of these forms of Tum’a does not transgress a Biblical command if he enters the site of the Temple. These include forms of Tum’a that do not invalidate a Nazir’s observance of his vow (which entails, among other restrictions, abstaining from Tum’a associated with contact with human corpses). They also include a person who touched a utensil that had been touched by somebody who became Tameh through contact with a corpse. People with these forms of Tum’a are proscribed from entering the site of the Temple by force of Rabbinic enactment, and if they do, they receive Malkut.
One who throws impure utensils into the area of the Bet Ha’mikdash is not liable to Karet, but does receive Malkut.
This prohibition is binding upon both men and women, and is applicable even nowadays, despite the absence of the Bet Ha’mikdash. In warning of the destruction of the Bet Ha’mikdash in the Book of Vayikra (26:31), Hashem says, “Va’hashimoti Et Mikdeshechem” – “I shall lay your Temples desolate,” implying that even in its state of desolation, the Temple still retains its status as a “Mikdash,” a sacred site. As such, the prohibition against entering the site of the Bet Ha’mikdash in a state of Tum’a applies even after the Temple’s destruction. Therefore, today, when we are all presumed to have impurity, we are not permitted to enter the area where the Bet Ha’mikdash stood. (Indeed, there are signs in Jerusalem warning observant Jews of where they may not proceed, in order to avoid transgressing this prohibition.)
The Gemara in Masechet Erubin addresses the situation where the carcass of a Sheretz (rodent that emits Tum’a) is discovered in the area of the Bet Ha’mikdash. As the Torah forbids bringing impurity into the area of the Temple, the carcass must be taken out of the area. Rabbi Yohanan, as the Gemara cites, taught that the way this is done is by a Kohen wrapping the rodent’s carcass with his Abnet (belt), and then carrying the carcass outside the area of the Temple. This way, the Kohen does not become Tameh, and only the Abnet becomes Tameh.
The Minhat Hinuch raises the question of why it should be permitted to actively defile the Abnet in the area of the Mikdash, causing it to become a Rishon Le’tum’a (something which came in contact with an original source of impurity). This will have the effect of bringing, in a sense, an impure article into the grounds of the Bet Ha’mikdash. We would have assumed, the Minhat Hinuch writes, that it is preferable to passively allow the carcass to remain in the area of the Mikdash, rather than actively bring an additional Tum’a to the Mikdash by defiling the Kohen’s garment. Evidently, the Minhat Hinuch answers, the Gemara understood that the Torah prohibition does not apply to a Rishon Le’tum’a. It is forbidden to bring an Ab Ha’tum’a (an original source of impurity, or a person or utensil that came in direct contact with a human corpse) into the area of the Temple, but not a Rishon Le’tum’a. Therefore, causing the Kohen’s garment to become a Rishon Tum’a is permissible on the level of Torah law, and this should be done for the sake of removing the carcass, which is an Ab Ha’tum’a. (The Kohen himself does not become impure by touching the garment, because a Rishon Le’tum’a brings impurity only to food and liquids, and not to people or utensils.)