What do we learn from "ka'Chometz la'Shinayim uche'Ashan la'Einayim"?
Shabbos 111a: This teaches that vinegar harms teeth 1 (just like smoke harms the eyes).
R. Yonah: Even though sometimes vinegar is useful for a cure, and sometimes smoke is needed, and they ignite a fire to sit opposite it, benefit from them perforce harms other limbs.
Shabbos 111a: Our Mishnah forbids on Shabbos vinegar for aching teeth. This implies that vinegar helps teeth! The verse discusses vinegar from unripe grapes; the Mishnah discusses vinegar from proper grapes. Or, vinegar helps for a wound, but it loosens healthy teeth [from the gums].
What is the comparison to those who sent an Atzel?
R. Yonah: Sometimes one needs to send him, and there is benefit from him, and it is better to send him than to refrain. However, there will be a mishap. Due to laziness, he will not hearken to the sender and guard his words in his heart, or will not understand his words, or he will be lazy and delay on the way. Perhaps the entire Shelichus will not benefit (for had he sent a diligent Shali'ach, the full Shelichus would have been done). Now that he sent an Atzel, "v'Chesron Lo Yuchal Lehimanos" (Koheles 1:15). The benefit cannot occur without damage, just like regarding vinegar and smoke.
Malbim: One who eats something vinegary in order to arouse appetite, Just the contrary, this sets his teeth on edge! Even though he is aroused to eat, he cannot chew the food! Also smoke to the eyes - if one burns sparks to illuminates in the house, even though there is light, it strikes the eyes and one cannot see. So one who sends an Atzel - not only will he not get the desired result, he will even ruin the purpose. All this is a metaphor for one who is lazy in the general Shelichus - he was sent to this world to perfect his Nefesh!
Why is this verse amidst Midos of a Tzadik and a Rasha?
R. Yonah: Verse 25 said "v'Tzadik Yesod Olam", and verse 27 says "Yir'as Hashem Tosif Yamim." Our verse is a Mashal for the work of Torah and Mitzvos. Those who are vigorous in them, they are Sheluchim of Hashem - "va'Yishlachacha Hashem b'Darech" (Shmuel I, 15:18), "Ki Hashem Shalchani La'asos" (Bamidbar 16:28), "Lehashiv Amarim Emes l'Sholechecha" (below 22:21). The verse comes to warn to be zealous in Mitzvos and to demean laziness. It informs that a Mitzvah that requires toil, it can be done properly only with Zerizus. If an Atzel does it, he will omit part. He will not be saved from damage to his soul and punishment, even though he did the Mitzvah and will be rewarded. Also when he learns, he will not understand all his teachers' words; he will constantly err in ruling. 'When Zechuchei ha'Lev 1 became rampant, dispute increased in Yisrael' (Sotah 47b). 2
Rashi (47b): These are haughty people. (R. Yonah implies that they are lazy. Perhaps they rely on their own understanding, like Me'iri explained there, due to laziness. -PF).
R. Yonah: Also Tefilin needs Zerizus; if he diverts his mind, he will be punished. He may not pass gas or sleep in them; the Mitzvah is the entire day. However, one who engages in Mitzvos is exempt from [other] Mitzvos. All obligations to Hashem require Zerizus; laziness brings sin. When one declares the Creator's unity, if his mouth and lips honor Him, but his heart is far from Him, his sin is great. At the time of Tefilah, he may not veer after his heart and affairs. One who speaks to the king or counselors of the land would not do so!
