Who are "Pesayim"?
Rashi: They are those who are enticed via enticers and heretics.
R. Yonah: They are people of weak Sechel. They are enticed via enticers and deceivers. It includes also people with errant mindsets, and those whose desires make their ways errant. You see some people who think that everything that they desire is proper; they see nothing detrimental about it. This is due to their weak Sechel; desire draws them to it, and blinds their eyes. If their desires would not rule over 1 them, and they did not consent to be drawn after it, their mindsets would not be errant. 'Anyone who accepts his Yetzer's enticement, he falls to Gehinom' (Eruvin 19a). "V'Elecha Teshukaso v'Atah Timshal Bo", "Ki Yetzer Lev ha'Adam Ra" (Bereishis 4:7, 8:21). [The Yetzer ha'Ra] requests matters from [the person], and yearns that he give to him all that his eyes. The Yetzer cannot fulfill its desire without the consent of the intellectual Nefesh. "V'Atah Timshal Bo" is like "v'El Ishech Teshukasech v'Hu Yimshal Bach" (ibid. 3:16). Therefore the Nefesh is punished when it wants to follow desire.
Malbim: He is one who is enticed to the path of folly, without Da'as.
Ma'alos ha'Torah (DH Od Yadu'a): It is anyone who does not engage in Torah.
Perhaps the text should say Yamshichu (draw), in place of Yamshilu. (PF)
Why does it say "Te'ahevu Pesi"?
Rashi: Pesi is a noun - enticement. Its grammatical form is like Kli, Keri, Shefi (R. Yonah - "Beis ha'Meri" (Yechezkel 24:3).
R. Yonah: Ahavah is choice - "Ki Chen Ahavtem Bnei Yisrael" (Amos 4:5), "Ahavu Lanu'a" (Yirmeyah 14:10). Fools choose ways of enticement, and err to say that they are straight ways.
Malbim: He loves to be enticed without Da'as.
What is the meaning of "v'Letzim Latzon Chamdu Lahem"?
R. Yonah: Letzim are people who belittle every matter, mock people and speak Leshon ha'Ra. There are two sources for this Midah. (a) It is from the root of bad Midos of the Nefesh, from cruelty and pride, like we will explain "Zed Yahir Letz Shmo" (refer to 21:24:1:2 and the note there). (b) It is totally casting off the yoke of Shamayim. Because there is no yoke of fear on him, and no fear of Elokim in his heart, his heart is sent to frolic and mock. "Al Tislotzatzu Pen Yechzeku Mosereichem" (Yeshayah 28:22) - Midah k'Neged Midah, for you cast off Shamayim's yoke, and He will make your yokes heavier and strengthen your ropes (Avodah Zarah 18b). It says "Chamdu Lahem", for scoffing is due to Midos of the Nefesh that desires.
Malbim: Letzim mock Chachmah, for it does not have proofs from Da'as. He does not hate Chachmah, for he does not know it clearly. They do not receive it via Musar and Yir'as Hashem, because they wanted to mock words of Emunah for which there is no proof.
Who are "Kesilim"?
R. Yonah: They are people of bad actions. They transgress to fulfill their eyes' requests for pleasures and delights. Know that there are three powers of the Nefesh. (a) It sprouts and grows. This is the same in man, animals, trees and vegetation. This power is found in the liver, and it is called Nefesh - "k'Nafshecha Savecha" (Devarim 23:25), "Tzadik Ochel l'Sova Nafsho" (below, 13:25). (b) The power of desire. Those who spoke about nature, they mentioned Midos of the Nefesh born from this power. Also other living beings have this desire to find their needs to grow, also to damage and win. Some call this 'the animalistic Nefesh.' It is in the heart, and it is called Ru'ach - "v'Nishmartem b'Ruchachem v'Lo Sivgodu" (Mal'achi 2:16), "ha'Oleh Al Ruchachem" (Yechezkel 20:32), "Kol Asher Nadvah Rucho Oso" (Shemos 35:21). (c) The power of Sechel. It is the foundation of the Nefesh. It is called Kavod - "Urah Chevodi", "Lema'an Yezamercha Chavod" (Tehilim 57:9, 30:13). It is called also Yechidah and Neshamah; it is only in man, but not in other living beings.
Do only Kesilim hate Da'as?
R. Yonah: Yes. One who pursues needs of the power of growth, he distances greatly from the power of Sechel, for he is drawn after physicality and what come from the ground. Also one who pursues needs of the power of desire is distanced from the power of Sechel, but the former distances him more, and can entice him to desire to sin with food and intimacy. Sechel will not rule over with Yir'as Hashem. Therefore it says that Kesilim hate Da'as; it did not say so about Letzim, for they do not pursue pleasures as much. Also Kesilus includes bad Midos of the Nefesh and desire to indulge in bodily pleasures.
Malbim: Yes. The Kesil knows the laws of Chachmah, and departs from them due to his desire, for they oppose the desires of his heart. They are like a harness to muzzle the heart's desires. In this way he is worse than the Letz, who mocks only what he cannot know clearly.
Our verse rebukes Pesayim, Letzim and Kesilim. Below, it says "Al Yochach Letz Pen Yisna'echa" (9:8), "b'Aznei Chesil Al Tedaber" (23:9)!
R. Yonah: The primary Mitzvah of rebuke is for a Pesi, Na'ar, and a Chacham or Navon who happened to err. However, if there are reasons to rebuke a Letz or Kesil, to tell them the punishment, perhaps their hearts will be humbled. However, if you will tell them 'this matter is sin 1 ', they will disgrace your words. Until their hearts are humbled, they will not hearken to warning or Chachmah.
Without telling them the punishment. (PF)