How does one seize Musar?
Rashi: He holds onto Torah. This is like "v'Hachaziki Es Yadech Bo" (Bereishis 21:18), "va'Yishlach Yado va'Yachazek Bo" (Shemos 4:4).
R. Yonah: Even if you know Chachmah, you must demean evil.
Malbim: The desires of the heart oppose the laws of Chachmah. The images of the heart lean to evil, the opposite of Chachmah. You need Musar to bind the powers of the Nefesh, lest they veer you from the ways of Chachmah. Musar is Yir'as Hashem - "Yir'as Hashem Musar Chachmah" (15:33). Via Yir'as Hashem, he fears to transgress the laws of Chachmah that Hashem gave. However, also this Musar and Yir'as Hashem is not aroused in man's heart by itself. He must strengthen himself in it with all his strength, lest it depart from his memory for a moment. If you will slacken, it will depart from your memory.
What is the meaning of "Nitzreh"?
Malbim: You will guard Chachmah. Via strengthening in Musar, Hashem will guard the laws of Chachmah in Your heart.
Why does it say "Ki Hi Chayecha"?
Malbim: Chachmah is life of the Nefesh - "v'Yihyu Chayim l'Nafshecha" (3:22). Without Chachmah, there is not life of the Nefesh, only animalistic life, which is not Chayecha (human life).
