Why did he say "Lema'an Asaprah
Radak: When I will be saved from my haters, I will tell all Your praise
Why is there a Yud in "Tehilasecha"?
Radak: This shows that there will be many praises. Even though Tefilah is feminine, and the plural should say Tehilosecha with a Vov, and an added Yud indicates plural for masculine nouns, We find like this - "Nileis b'Rov Atzasayich" (Yeshayah 47:13).
How can David tell all Hashem's praise? "Mi Yemalel Gevuros Hashem [Yashmi'a Kol Tehilaso]" (106:2)!
Radak: David will tell the praise for all the famous salvations that Hashem did for him from his afflictions and enemies. That verse teaches that no one can tell all His miracles for Yisrael in all the generations. Also an individual, the miracles, benefits and Chasadim that Hashem does with him, one cannot tell them - "Agidah va'Adaberah Atzmu mi'Saper 1 " (40:6). Often, Hashem does a miracle for a person, and he knows it only after he contemplates! Ba'al ha'Nes (for whom the miracle was done) does not recognize the miracle (Nidah 31a)!
That verse discusses "Nifle'osecha u'Machshevosecha Eleinu" (for Yisrael)! (PF)
Why will he tell in Sha'arei Bas Tziyon?
Radak: That is where [Hashem's] honor dwells.
Why did he use an expression of Gilah, and not of Simchah?
Malbim: Gilah is rejoicing over a new matter. You will do for me new salvations; I will have a new Gilah, and thank You with a new Shirah.
Which salvation does he discuss?
Radak: It is the salvation that You will bring for me from every hater.
