What are "Chasdi" "Metzudasi", "Misgabi" "Mefalti Li" and "Magini"?
Rashi (18:3, Shmuel II, 22:2-3): Metzudasi is my fortress. Mefalti - He saves me with the army of Yisrael in war, and He saves me when I am alone, e.g. from Yishbi b'Nov. Misgabi is my support.
Malbim: Chasdi is accepting me in His fortress and strong cities [to save me from the enemy]. Misgabi and Mefalti are salvation from an enemy that finds me before I reach the fortress. Magini is a shield from the enemy's arrows even when I do not flee. Malbim (18:3) Misgabi - He gives to me strength at the time of battle.
The suffix Yud in "Mefalti" means 'mine'. Why does it say also "Li"?
Radak #1: This is additional explanation.
Radak #2: The suffix Yud is extra, like in "ha'Magbihi Lasheves" (113:5).
What is the meaning of "ha'Roded Ami Tachtai"?
Rashi #1: He spreads out my nation to lie in its place, like "Shote'ach la'Goyim" (Iyov 12:23). Roded is the Targum of Roka; the Targum of "va'Yrak'u" (Shemos 39:3) is u'Redido. Radak - "Ami" is like Amim. Alternatively, it means my nation, i.e. Sha'ul and his supporters.
Rashi #2: He weakens nations under me. In an accurate Sefer, the text is "Ami". However, based on Mesores, this is one of three places in which it is written "Amim", and we pronounce it "Ami" 1 . The Mesores says that we pronounce Tachtai "Tachtav".
Malbim: Also my kingship over Yisrael is via Him.
