What is the consequence of "Musar Hashem Beni Al Tim'as"?
Rashi: If afflictions come upon you, they should be dear to you.
R. Yonah: This is a wondrous matter in Bitachon. If a Ba'al Tzedakos and Mitzvos sees that he does not succeed in wealth, or Hashem's rebuke comes, he strengthens himself in Bitachon and does not despise His Musar. He knows that it is for his benefit, more than reward of success in wealth and serenity. Hashem wants to cleanse him of all guilt and sin, to great his reward in the world of recompense. Serenity of this world is not important. Man's days are like a fleeting shadow. At the end, it is as if it was not. Even if he would live 2,000 years, one moment of contentment in the world to come is better than all life in this world. Man does not know what is good for him. Hashem knows what is good for him - serenity or afflictions!
Malbim: Wherever it says Musar and Tochachah about people, Musar is forced or via afflictions, and Tochachah is clarification via intellectual proofs. Therefore it says about Musar "Al Tim'as", for people normally despise afflictions. Regarding Tochachah it says "v'Al Takotz", for one does not despise it itself, since it is with Sechel and Da'as. However, sometimes one who hears it is repulsed. Regarding Hashem, sometimes Tochachah is via afflictions to fix a prior sin. "Tochachah" comes for the afflictions that will return him to the good path in the future, like afflictions of love that Chazal discussed. Whomever Hashem desires, He crushes him with afflictions (Brachos 5a). A stipulation of these afflictions is that he accepts them with love and puts to his heart to improve his way.
Why does it say add "v'Al Takotz b'Sochachto"?
Rashi: This is an expression of revulsion, like "Katzti v'Chayai" (Bereishis 27:46).
R. Yonah: Do not be pained by rebuke. Accept it with love, like Chazal said, it says about one who is disgraced and does not disgrace
Koheles Zuta: "Al Ta'amod b'Davar Ra" (Koheles 8:3) teaches that we begin and end with good matters. One may stop in the middle of the Brachos. Or, we learn from "Imo Anochi v'Tzarah" (Tehilim 91:15) - Hashem does not want to be blessed amidst curses against His children.
