We arrive at Mishnah 6 in chapter 9 of tractate Sanhedrin, the final Mishnah in the chapter. After dealing with the way in which a court can bring about the death of a person without using one of the four regular methods of execution by the court, the final Mishnayos in the chapter come and teach about additional ways, which are actually outside the legal process - the killing of a person not through the court and not in the regular course of a legal process at all. This is the system of laws known in the language of the Mishnah: "Kana'in poge'in bo" - zealots strike him.
The basis of the law of zealots:
A zealot is a person who is extreme in his devotion to Hashem, who lives his entire life for the sake of the honor of Heaven. When he sees acts that harm the honor of Heaven in an extraordinary way, he is driven to take action and stop it, whatever the cost may be. The word "poge'a" in this context means actual killing, even though it usually just means meeting or encountering.
Three specific examples are brought in our Mishnah, and they are permitted by virtue of a halachah given to Moshe at Sinai - a special tradition for each of these three transgressions. One who acts as a zealot in these cases has the status of a pursuer, which means that the one about to be killed is allowed to defend himself; and if he defended himself and killed the zealot, he is not considered a murderer, as he acted within his right to defend himself.
For the halachah does not actually grant an official permission, but rather an exemption. It is not a halachah that one must kill the transgressor; we are talking about a zealot who, at the moment of the act, is unable to see the halachah out of sheer moral outrage, and if he indeed kills the perpetrator of the extreme act - he will receive an exemption. A fundamental condition for this: that the zealot acted without asking. Had he approached a court and asked what he should do, they would have answered him: "Do not do anything." It is only because he acted on his own accord that, after the fact, the court will exempt him. This is, therefore, an exceptional system of laws, standing to some degree outside the basic framework of the entire tractate.
The three cases in the Mishnah:
"Hagoneiv es hakasvah" - one who steals the kasvah - the kasvos are the vessels that were used to separate between the twelve loaves of the showbread on the table in the Sanctuary, like sorts of tubes, so that they would not become moldy and would not stick to one another. This detail itself makes no difference: the kasvah was chosen specifically because it is a small, cheap, and insignificant item, which represents any vessel of the Temple vessels. One who sees a person stealing a vessel from the Temple may be filled with rage - how could a person do such a thing to Hashem, to steal His vessels in His house and right in His presence, so to speak - and if he rises and beats him to death, he will be exempt.
"Vehamkalel bakosem" - and one who curses by a sorcerer - this expression is not to be translated literally. The intention is to one who curses Hashem by mentioning the name of an idol. Unlike the blasphemer, about whom we learned, who mentions one of the seven Names in order to strike and attack Hashem, Heaven forbid - here the person does not mention the Name itself but another idol. This is a negative prohibition, just as stealing is a negative prohibition, and it carries no death penalty at all. "Kosem" means a sorcerer, a person who engages in witchcraft. But if the one who hears the kosem doing this act of witchcraft, in which he tries to attack Hashem using an idol, rises up out of rage and attacks him and even kills him - the attacker, the zealot, emerges exempt.
"Vehabo'el Aramis" - and one who cohabits with an Aramean woman - this law is learned explicitly from the act of Pinchas, who saw Zimri, a prince in Israel, lying publicly with Kozbi the Midianite. Three conditions are required for this:
In public: In front of ten Jews. The intention is not specifically ten men, as this is not a matter of sanctity that requires a minyan, but rather ten Jews - men and women alike.
An Aramean woman: Not just any gentile woman, but specifically an idol worshiper. If the woman is in the category of a ger toshav, a God-fearing person who does not worship idols - this law does not apply here.
At the time of the act: Only when they are actually together.
When the three conditions are met, at the time that they are together in public in the eyes of people with that idol worshiper, one who is so shocked by the desecration of Hashem's Name that he attacks and kills them - will be exempt. This is what the Mishnah said: "Kana'in poge'in bo" - zealots strike him. The zealot is allowed to attack them and even kill them, and he does not face justice for it and is not punished for his act.
A kohen who served in a state of tumah:
Another case brought here is not from the law of zealots striking him, but a law similar to it: a kohen who intentionally performed service in the Temple when he was tamei. This too is a negative prohibition from the Torah, and it carries no death penalty from the court. However, if his fellow kohanim see him, and he knows that he is tamei and serves anyway, the Mishnah says: "Ein echav hakohanim mevi'in oso leveis din, ela pirchei kehunah motzi'in oso chutz la'azarah u'mefatze'in es mocho begizirin" - his brother kohanim do not bring him to court, rather the young kohanim take him outside the courtyard and split his brain open with blocks of wood.
His fellow kohanim do not bring him to judgment and punishment, but rather the young kohanim - the young kohanim whose beards have begun to sprout, as we have seen in many Mishnayos - take him outside the courtyard, for they are about to kill him, and one must not kill in the courtyard because one must not bring tumah there. And why specifically the young ones? First, such an act is not befitting the honor of the older kohanim; and second, such a sight leaves an indelible impression on the young ones.
"U'mefatze'in es mocho begizirin" - and they split his brain open with blocks of wood - they shatter his skull and crush his brain with gizirin, which are blocks of wood. This is not because of any special quality of the blocks of wood, but because weapons were not commonly found in the Temple, whereas the logs of the arrangement - the blocks of wood used for the fire on the altar - were scattered around. Therefore they would grab them, like sorts of clubs, and shatter his head with them. A harsh business.
A non-kohen who served in the Temple:
To conclude, the Mishnah asks about a non-kohen who served in the Temple: What is the law regarding someone who is not a kohen and decides to enter and perform the service as if he were a kohen?
"Rabbi Akiva omer" - Rabbi Akiva says: by strangulation. In his opinion, this sin is added to the list of thirty-six transgressions punishable by execution that we enumerated in the seventh chapter, making them thirty-seven.
"Vachachamim omerim" - and the Sages say: by the hands of Heaven. The punishment is only death by the hands of Heaven - the person indeed deserves to die, but the court does not carry out the execution, rather Heaven does this itself.
The basis of the dispute:
The basis of the dispute is technical. The verse states: "Vehazar hakarev yumat" - and the non-kohen who approaches shall be put to death. According to Rabbi Akiva, there is a gezeirah shavah here, a tradition to derive this from another mention of death: in the Book of Deuteronomy it is stated, "Vehanavi hahu o cholem hachalom hahu yumat" - and that prophet, or that dreamer of a dream, shall be put to death - referring to a prophet who instructs to engage in idol worship, and we know that his punishment is strangulation. Therefore, we compare the word "yumat" in our verse to the word "yumat" regarding the false prophet, and deduce that here too it is strangulation.
But the Sages disagree and derive their ruling from the adjacent passage, which precedes the verse "Vehazar hakarev yumat" - the incident of the congregation of Korach, the two hundred and fifty men who participated in the rebellion, about whom it is stated: "Kol hakarev hakarev el Mishkan Hashem yamut" - anyone who comes near, who comes near to the Tabernacle of the Lord, shall die. Since the passages are adjacent to one another, just as there the punishment is only death by the hands of Heaven, so too in "Vehazar hakarev yumat" - it means death by the hands of Heaven, and Heaven carries this out.
Rabbi Akiva rejects this derivation, because in our verse it is stated "yumat", whereas regarding the congregation of Korach it is stated "yamut". However, the Sages hold that it is preferable to derive from there, even though the wording of the verses is different, because we are comparing two ordinary people to one another rather than to a prophet, and therefore the derivation is even better.
The halachah in this final case follows the Sages: death by the hands of Heaven. Death by the hands of Heaven is a lighter punishment even than kares - it means premature death, but the death itself atones for the sin. This is in contrast to kares, where if the person does not repent, he is completely cut off: childless, disconnected from his children, and even cut off and disconnected from the World to Come if he does not repent before his death.
In summary: In this final Mishnah we learned about execution outside the judicial process - the law of "kana'in poge'in bo" (zealots may attack him), which is not an outright permission but an ex post facto exemption for a zealot who acts without asking, and its three cases: one who steals the kasva, one who curses using an idol, and one who cohabits with an Aramean woman under its three conditions. We also learned about a similar law, a kohen who served in a state of tumah, where the young kohanim take him outside the courtyard and split his skull with wooden clubs, and about the dispute between Rabbi Akiva and the Sages regarding a non-kohen who served in the Temple - strangulation or death by the hands of Heaven, where the halachah follows the Sages.