What is the meaning of "mi'Pri Fi Ish Yochal Tov"?
Rashi: In the reward of his Torah, he eats good in this world, and the principal is intact for him in the world to come.
R. Yonah: If he rebuked him, he has the reward of rebuke.
Above, it says "mi'Pri Fi Ish Yisba Tov" (12:14). Why does it say here "mi'Pri Fi Ish Yochal Tov"?
Malbim: Here it teaches that his mouth is Eitz ha'Da'as Tov v'Ra. The mouth hints to Chachmah, the lips to Da'as, and the tongue to Binah; 18:20 discusses all of them. The fruit of the mouth is Pri Eitz ha'Da'as Tov v'Ra. Chachmah has two ways, e.g. pride and humility, mercy and cruelty. One must conduct them with Chachmah. One who uses Chachmah for good, he will eat the good from the tree. "Mi'Pri Fi Ish Tisba Bitno" (18:20) - his stomach will be satiated from the fruits of his mouth (Chachmah), for good or for bad, according to the preparation. Also refer to 18:20:1:3, 18:21:1:3, 18:21:2:3.
Malbim: According to the simple meaning, "mi'Pri Fi Ish Tisba Bitno" discusses the fruits of one who speaks in Torah and Tefilah, and here discusses speech in Derech Eretz. He must be careful not to profane what leaves his lips. Then, he will eat Tov; he will be faithful, and eat from his toil. Above it says Yisba, which refers to reward of the Nefesh - "v'Hisbi'a b'Tzachtzechos Nafshecha" (Yeshayah 58:11). Achilah means that he will have what to eat well.
Why does it say "v'Nefesh Bogedim Chamas"?
Rashi: The desire of traitors is theft. Nefesh is [desire,] like "Im Yesh Es Nafshechem" (Bereishis 23:8), "Al Titeneni b'Nefesh Tzarai" (Tehilim 27:12).
R. Yonah: The desire of traitors is theft. How can they rebuke their sons?! Since his desire is theft, and a Rasha's desire is evil, his son is not averse to follow these Midos. He will not hit his son to make him depart from them. Even if he does rebuke, it is known that his heart is not with his rebuke. He cannot resolve the words so they will be heard.
Malbim: A traitor, who uses his Midos the opposite of the way of Chachmah, from the fruit of his mouth he will eat theft. He will use all his Midos for evil, via the snake that entices for evil. This is called Boged. He does not guard what comes out of his mouth and his promise. The Nimshal is, he does not use the way of Chachmah like it should be used. Chamas is theft of everything proper, both monetary and in Midos.
Malbim: The simple meaning is, one who does not guard his Emunah - this is Boged - his Nefesh will eat theft.
