Radak: They are people great in Torah - Do'eg was Av Beis Din - "Abir ha'Ro'im Asher l'Sha'ul" (Shmuel I, 21:8), "va'Achitofel Yo'etz" (Divrei ha'Yamim I, 27:33), "the counsel of Achitofel

Rashi: It is Al Nafshi.

Radak: It is about my Nefesh, like "Imri Li Achi Hu", "va'Yish'alu Anshei ha'Makom l'Ishto" (Bereishis 20:13, 26:7) and similar verses. Many Chachamim, e.g. Achitofel, correctly thought that this was David's punishment for the episode of Bas Sheva. They also thought that he will never return to his kingship. Therefore they supported Avshalom and rebelled against David and said that he has no share in the world to come. Therefore, he said "l'Nafshi".

Malbim: There were two groups of Avshalom's counselors. Some wanted to kill David, like Achitofel's counsel; they were against "Nafshi". Others wanted only to take kingship, but leave him alive, like Chushai ha'Archi's counsel. They are "ha'Kamim Alai" (verse 2).

Rashi: It is because he had Bi'ah with a married woman.

Radak, citing Shocher Tov: Hashem will not save him from Avshalom, and there is no salvation for his Nefesh in the world to come. The extra letter Sav in "Yeshu'asah" hints to two salvations. Similarly "Ezrasah" (44:27) is great help, and similarly regarding "Tavosah" (Devarim 33:17), "Nifle'asah" (Shmuel II, 1:26) and "Hechbe'asah" (Yehoshua 6:17).

Radak #1: Most Meforshim say that it is like 'forever', and so Yonason translates it in Chabakuk (3:3) 'l'Almin'. We find that it often means so in our Tefilos.

Radak citing Ibn Ezra: It is like 'Emes'.

Radak #2: It refers to raising, like "Solu Solu ha'Mesilah" (Yeshayah 62:10). It is an instruction for the singer to raise his voice ¹ . It is found only in this Sefer and in Chabakuk's Tefilah, which was a Shir - "la'Menatze'ach bi'Neginosai" (Chabakuk 3:19).

Malbim (1): This Mizmor tells the war of Avshalom. It is divided into three; each part ends with "Selah".