Why does it say "Ta'avas Tzadikim Ach Tov"?
R. Yonah: One is considered to be a Tzadik only if he eradicates from himself every bad desire, and the only remaining wishes in his heart are for good. "Ach" shows that he nullified desires for evil, pleasures, authority and worldly follies. David said "Hashem Negdecha Kol Ta'avasi" (Tehilim 38:10) - all my desire is revealed in front of You. A bad desire will not accompany it. Envy, lust and [craving] honor take a man out of the world (Avos 4:21).
Malbim: Ta'avah is unlike Tikvah. Mis'aveh has no hope to attain the matter; he merely desires. Mekaveh hopes to attain the matter. Ta'avah of the Rasha is Ra. (a) He desires acquisitions that are not his, and extortion, theft and forbidden matters - "Nefesh Rasha Ivesah Ra" (21:10). (b) He does not attain his desire - "Ta'avas Resha'im Toved" (Tehilim 112:10). However, Ta'avas Tzadikim is only good. (a) He desires only good - "l'Shimcha ul'Zichrecha Ta'avas Nafesh" (Yeshayah 26:8). (b) Hashem gives his desire - "v'Sa'avas Tzadikim Yiten" (below, 10:24), "Ta'avas Anavim Shamata Hashem" (Tehilim 10:17). It is good that Hashem fulfills it - "Ta'avah Nihyah Te'erav l'Nafesh" (below, 13:19).
Why does it say "Tikvas Resha'im Evrah"?
Rashi: They are assured and hoping to go to Gehinom.
R. Yonah #1: Not only do Resha'im desire evil - they hope and prepare themselves for it amidst their great desire. There cannot be desire without hoping - "Li Kivu Resha'im Le'abedeni" (Tehilim 119:95). Their hope is Evrah - the demise of people and evil [befalling them].
R. Yonah #2: Evras (anger of) Hashem is via Resha'im, for their hope is for evil.
Malbim: Also what Resha'im hope for and think that it is prepared in front of them to attain it, it is anger of two reasons. (a) They do not attain it - "v'Sikvasam Mapach Nafesh" (Iyov 11:20), "v'Sikvas Resha'im Toved" (above, 10:28). (b) The hope itself is evil - "Li Kivu Resha'im Le'abedeni." They hope for distress and affliction for everyone, amidst envy, or love of honor, that only they will remain serene. In the end, the distress comes against them. I explained above (10) that Resha'im do not have Tocheles (what they hope for is not sure to come), only Tikvah. Evrah is when anger passes the proper boundary.
