Why does it say "Al Tehi Tzadik Harbeh"? One should strive to be a great Tzadik!
Refer to 7:17:1:2.
Ibn Ezra: If you will pray from morning until evening, fast, and similar matters, you will veer from the way of civilization.
Rashbam: Do not be too virtuous, e.g. to be killed due to a light Mitzvah.
Rid: Do not say, I will not marry a woman, lest I stumble in Dam Nidah. I will not eat meat, lest I stumble in Chelev or Dam. I will not eat vegetables, lest I stumble in worms. I will not do business with people, lest I stumble in theft.
Metzudas David: Do not forbid what the Torah permitted, in order to make a fence 1 .
Mo'ed Katan 5a: "U'Shmartem Es Mishmarti" (Vayikra 18:30) - make a guarding for My guarding (fences lest you transgress Torah law)! Perhaps Metzudas David means not to forbid what the Torah explicitly permitted like the Taz (OC 588:5). Or, he discusses excessive fences. (PF)
What is wrong with being too wise?
Rashi citing Yuma 22b: [Sha'ul] judged a foolish Kal v'Chomer. If the Torah said to bring Eglah Arufah over one person [who was killed, why should we kill all these Amalekim, even children?
Ibn Ezra: You will veer from the way of civilization.
Rashbam: Refer to 7:16:1:3.
Ri Kara: Shlomo, said, I will increase [wives] and not veer my heart. In his old age "Nashav Hitu Es Levavo" (Melachim I, 11:4). Due to this, [most of] his kingship was removed [from his sons] and given to Yaravam.
Rid: Do not say, why should I have pleasures of this world, which pass - marital intimacy, eating and drinking, nice clothing and a nice dwelling. Rather, I will dwell in cracks in rocks, and fast all my days for the Creator.
Seforno: Do not make vows to find grace [in Hashem's eyes], unless needed to subdue your Yetzer.
Mesilas Yesharim (Perek 13): There is Perishus (separation) that we are commanded about it, and Perishus that we are commanded [to avoid it], lest we stumble in it.
Metzudas David: Do not be wiser than what Hashem's Chachmah decreed.
What is "Tishomem"?
Rav Sadya Gaon: You will come to prefer isolation and desolation.
Ibn Ezra: It is to veer from civilization, like people strayed in Edom and Yishmael. This is Nif'al conjugation. Some say, it is Hispa'el 1 ; the Dagesh in the Shin is in place of a missing Tov (it should say Tishtomem), and not in place of a Nun for Nif'al).
Rashbam: You will be desolate (missing) from the world.
Ri Kara: You will be desolate [from your kingship], like Sha'ul and Shlomo.
Rid: It is to afflict and make himself desolate.
Metzudas David: You will be isolated and separated from people, for no one will join to you due to your excess separation.
Ibn Ezra, Rashbam: Its grammatical form is like Techonen - "Tibaneh v'Sikonen" (Bamidbar 21:27).
