What is the meaning of "Ki Chatas Kesem Meri v'Aven u'Serafim Haftzer"?
Rashi: Like 1 the punishment for evil and Terafim, so is the punishment for Haftzer (one who adds to the Navi's words).
Targum Yonasan: Like the liability of one who asks via witchcraft, so is the liability of one who rebels against Hashem's word 2 , and the liability of the nation that strays after idolatry, so is the liability of one who exceeds and adds to the Navi's words.
Malbim: Refusal to do Hashem's word is like witchcraft, for the primary sin is not being Tamim (purely faithful) with Hashem and His Nevi'im, to ask witches - "Ki ha'Goyim? El Me'onenim v'Kosmim Yishma'u v'Atah Lo Chen?; Navi mi'Kirbecha?. Elav Tishma'un 3 " (Devarim 18:14, 15). If he does not admit to his sin, and persists, it is as if he adds the sin of Terafim (idolatry)
Radak: The prefix Chaf is missing; it is as if it says k'Chatas?This is like "Lev Same'ach Yeitiv Gehah" (it is as if it says k'Gehah - a happy heart improves [health] like a cure).
Radak: This is a great sin, for he removes his Emunah from Hashem and trusts in witchcraft - this is Meri (refusing to do what Hashem commands). After transgressing, he denies and says that Hashem cannot help or harm, therefore he does not fear Him, and transgresses His word. This is like idolatry!
This is right after "Tamim Tihyeh Im Hashem."
What is "Haftzer"?
Rashi: It is increase. "Va'Yiftzar Bo"(Bereishis 33:11) - he increased words (of coaxing and supplication).
Why does it say "va'Yim'ascha mi'Melech"?
Radak: The Vov is superfluous, like "va'Yisa Avraham Es Einav" (Bereishis 22:4). Because you despised Hashem's word, He despised you from being king.
