Why is this Mizmor after the first one?
Radak citing Brachos 9b: Some say that this is a continuation of Tehilim 1 1 .
Radak: (They are different Mizmorim.) We do not know the reason why David ordered them the way he did. They are not in order of when the events occurred; the next Mizmor is about Avshalom, and afterwards are several Mizmorim about events that were long before the episode of Avshalom! "Bi'Hyoso va'Me'arah Sefilah" (Tehilim 142) was in the days of Sha'ul, and it is towards the end of Tehilim! This Mizmor was at the beginning of David's kingship (refer to 1:2:2:2).
Malbim: Mizmor 1 ended with the doom of the Rasha; he is like chaff that the wind blows it. There is hope for it only if it guards grain and guards a Tzadik. If so, why are nations excited to rebel against Hashem's anointed and His nation Yisrael? The nations will endure only if they serve Hashem and David, His king!
Ohr Yisrael (Monsey 5758:12, p.144-152): Nochrim divided all Seforim of Tanach into chapters in the 13th century. It became accepted within Yisrael, to facilitate countering claims of the Komerim in the debates that Yisrael were forced to take part in. (This Gemara is one of the sources that Tehilim was already divided into Perakim [via David]. Similarly, Yirmeyah divided Eichah into Perakim; each of the first four Perakim is a single or three-fold Aleph-Beis. Eichah Rabah (Pesichah 28) says that it has five Perakim; refer to Yirmeyah 36:32:1:2-3. - PF)
What agitated the nations?
Rashi: Chazal said that it was due to Melech ha'Mashi'ach. Radak (12, from Brachos 7b) - this Mizmor discusses Gog and Magog; "Meshicho" (verse 2) is Melech ha'Mashi'ach. It is better to say that the Mizmor discusses David himself. 1
Rashi: It was due to David. "The Pelishtim heard that Yisrael anointed David
Brachos 7b and other sources say that it is due to the war of Gog and Magog. Avodah Zarah 3b says that in the days of Mashi'ach, they will come to convert, but will retract when Gog and Magog come against Hashem and His Mashi'ach. (PF)
Is there a difference between Goyim and Le'umim?
Malbim: Yes. Goy is a collection, without concern whether or not they have the same creed. Le'um is when they are united under a particular creed. The nations' bond against [David] was both theological and civil - "Al Hashem v'Al Meshicho"; refer to 2:2:3:2. The Goyim were agitated to rebel against Malchus Beis David, and the Le'umim, regarding creed, had thoughts against the doctrine and Mitzvos of Hashem.
Why does it say "Yehgu Rik"?
Radak: When they came to war, they spoke haughtily, for they defeated Yisrael in war and Sha'ul and his sons died, and there was a great plague amidst the nation. There was no other king in Yisrael from when Sha'ul died. All their words are Rik (empty)!
