What do we learn from "Yitamu Chata'im Min ha'Aretz"?
Brachos 10a: Chata'im (sins) will cease, and not Chot'im (sinners)! Therefore, one should not pray that sinners die, rather, that Hashem help them to repent.
Rashi: Chot'im (sinners) will cease. 1
Radak (35, citing Ibn Ezra): The author requests that sinners be finished, because they do not thank His honored name, and do not understand His deeds.
Why does Rashi explain like R. Meir initially held? The Gemara implies that he retracted! (Refer to 104:35:1:1 - PF.)
What do we learn from "u'Resha'im Od Einam"?
Radak: After the sinners cease, new sinners will not come in place of them - "ume'Afar Acher Yitzmachu" (Iyov 8:19). In this world, if sinners cease, others come. Yemos ha'Mashi'ach will be different.
Malbim: Even though people will still sin amidst desire and the Yetzer 1 , there will not be Resha'im who sin b'Mezid, for they will recognize Hashem's Mishpatim and fear to sin.
Daf Al ha'Daf (Brachos 10a, citing Hegyonei Avos 4:24): After Resha'im are eradicated, then there is Simchah.
How does he resolve this with "Yitamu Chata'im Min ha'Aretz"? (PF)
Why does it say "Barchi Nafshi Es Hashem"?
Brachos 10a: David sang Shirah when he saw [through Ru'ach ha'Kodesh] the downfall of the wicked.
Why does it say "Hallelukah"?
Radak citing Brachos 9b: David said 103 Tehilim before saying Hallelukah, until he discusses the downfall of the wicked -- "u'Resha'im Od Einam... Hallelukah." Radak - Hallelukah is the greatest praise - it includes song and praise together. Kah is half of Hashem's name; for brevity, it is connected with Hallelu to make one word. 1
Radak: [My soul will bless Hashem;] all the nations should praise Him.
Radak (35, citing Ibn Ezra): The wise should praise Hashem.
Brachos 9b: In our Seforim, it is at the end of Tehilim 104; really, "Ashrei ha'Ish..." and "Lamah Ragshu Goyim" (which we call Mizmor 1 and 2) are one Mizmor.