1)
Why did David compose this Mizmor?
1.
Radak: It is when he first reigned, after he defeated the Pelishti kings; he was saved from wars of Yisrael and of Pelishtim.
2.
Radak (15, citing Rav Sadya Gaon): It refers to Yemos ha'Mashi'ach. It says "ha'Potzeh Es David Avdo" (10) because Mashi'ach's name will be David - "v'David Avdi Nasi Lahem l'Olam" (Yechezkel 37:25). Then will be all the good things - "Ein Peretz
2)
What is "Tzuri"?
1.
Radak, Malbim: It is my strength.
3)
Why does it say "Yadai la'Kerav Etzbe'osai la'Milchamah"?
1.
Malbim: Kerav is fighting the enemy nearby; Milchamah is from afar, via bow and arrows.