How are judgments prepared for Letzim?
Rashi: Hashem prepared punishments of Tzara'as for this Letz who speaks Leshon ha'Ra.
R. Yonah: This teaches that the Midah of prosecuting liability is worse than hiding sins, like I explained (refer to 19:28:2:2). Such Letzim deserve judgments of death, lest they destroy the world with their evil Midah. Also, there is no hope for a Ba'al Leshon [ha'Ra] to repent via rebuke after he became habituated. After the tongue became used to speaking the heart's desire and whatever crossed his mind, the tongue is not in his Reshus. Nachonu is past tense, Nif'al conjugation, like "veha'Mamlachah Nachonah b'Yad Shlomo" (Melachim I, 2:46). Anyone who trained his tongue to speak like his Nefesh's desire, he is called Letz. Shefatim are sentences of death, like "Arba'as Shefatai ha'Ra'im", "v'Asu Vach Shefatim" (Yechezkel 14:21, 16:41).
Refer to 17:10:3:4.
Malbim: False witnesses are punished Ka'asher Zamam 1 .
False witnesses are punished Ka'asher Zamam only if they are Zomemin! (There are other was to know that they lied, e.g. they testified that Reuven killed Shimon, and Shimon is found to be alive.) Perhaps Shamayim punishes all false witnesses Ka'asher Zamam, just like it punishes the four Misos Beis Din when Beis Din cannot do so (Kesuvos 30a). (PF)
Why does it say "u'Mahalumos l'Gev Kesilim"?
R. Yonah: Therefore, it is proper to give to a Rasha severe blows, for there is hope that he will subdue his Yetzer and rule over his limbs and deeds.
Malbim: [Evil] judges are punished with Makos from Shamayim.
