Why does the Torah add "ve'Lo Yosifu La'asos ... " here, but not above in Pasuk 6, in connection with the Navi Sheker?
Ramban: Because a Meisis is common, whereas a Navi Sheker is not.
Why does the Torah add "ve'Chol Yisrael Yishme'u ve'Yira'un"?
Ramban: Refer to 21:21:2:1**.
R. Bachye (in Pasuk 10): To teach us that, since the Torah's ways are merciful, Beis-Din should not execute the Meisis in order to take revenge, but rather, for the sake of having mercy on others.
Sanhedrin, 89a: To teach us the obligation to publicize the death-sentence of the Meisis. 1
See Torah Temimah, note 30.
Why does the Torah write "ve'Lo Yosifu La'asos" in connection with Meisis and Eidim Zomemin (here and in Parshas Shoftim, 19:20), and in connection with Zaken Mamrei (in Shoftim, 17:13) "ve'Lo Yezidun Od"?
Ran (in Sanhedrin 89a): Because whereas the reason one announces by Meisis and Eidim Zomemin is so that others should desist from following suite, the reason for announcing Zakein Mamrei is so that no-one should dispute the tradition.