What is the significance of "Chacham Lev Yikach Mitzvos"?
Rashi, from Sotah 13a: See how dear Mitzvos are to Moshe. All of Yisrael were engaged in despoiling Mitzrayim, but Moshe engaged in Mitzvos - "va'Yikach Moshe Es Atzmos Yosef" (Shemos 13:19).
R. Yonah: A Chacham Lev pursues and seeks Mitzvos. Even if he has no obligation, he contemplates how to find a Mitzvah to do it, like "Kechu Imachem Devarim" (Hoshe'a 14:3). He takes (does) Mitzvos with his hands, but does not glorify himself about them with his mouth. He says little, and does much (Bava Metzi'a 87a).
Malbim: Chacham is one who conducts according to the laws of Chachmah. The nature of the Yetzer ha'Ra of his heart opposes Chachmah. Everyone has a constant war with the Yetzer of his heart and his desires. Chacham Lev is one who already accustomed himself to the way of Chachmah until it became second nature for him, and the heart - the power of authority - is not aroused to evil at all. A mere Chacham hears or guards a Mitzvah, (conducts according to Hashem's command), but he does not take it. This is the only place where Lekichah is used with Mitzvos. Tzivuy is that the commander forces to do his command; the subject does so only due to him. If not for the command, his heart would do oppositely! Lekichah is taking the Mitzvah with desire and pursuing it. Only Chacham Lev can do so.
What is the meaning of "[v'Evil Sefasayim] Yilavet"?
Rashi: It is an expression of fatigue. The Sifri explains "va'Yhi ha'Am k'Mis'onenim" (Bamidbar 11:1) - they said, how much Nislavatnu on the road!
R. Yonah #1: Evvil is a sinner. He sins with his hands and mouth - deed is not enough for him. This shows that his sin is not due to the Yetzer overpowering and Ones of desire. Rather, his foolish heart concluded that there is no damage in sin. Yilavet is to be foolish (he foolishly informs about his sins), like "v'Im Lo Yavin Yilavet" (Hoshe'a 4:14) - if he does not contemplate his deeds, he is drawn to folly and desire, and sins with harlots.
R. Yonah #2: He boasts with his lips about his Tzedakah and Chesed, and does not do even a little.
Malbim: An Evvil is one who is unsure about the truth of the laws of Chachmah. Evil Sefasayim believes in Chachmah in his heart, but his external lips express doubts. He conducts with Chachmah, for his heart leans to believe it, but he did not resolve that there is no Safek about them. This is the opposite of Chacham Lev. Yilavet is to weary; alternatively, it is to waver - sometimes he veers from Chachmah.
