Why does it say "Lecha Dumiyah Sehilah"?
Rashi #1: Silence is praise for You, for there is no end to Your praise. One who adds praise, he detracts 1 !
Rashi #2: Refer to 65:2:2:2.
Radak: Dumiyah is hoping, like "Diminu Elokim Chasdecha" (48:10), from the roots Damah. It is also from the root Damam (silence) - "Domu Ad Hagi'enu Aleichem" (Shmuel I, 14:9). The praise that will be said to You in Tziyon, at the gathering of exiles, is waiting for You.
Radak (3, citing his father): This is like "Lo Damah Elav" (Yechezkel 31:8). The praise of You is proper only for You; You have more than they praise You. When they praise a person for his strength, wealth or Chachmah, the praise is not complete, for it always has some falsity.
Radak (3): It is silence, like "Al Dami Lach" (83:2). I.e. praise is dumbstruck to You, compared to Your awesome deeds, which praise cannot 'capture' (properly describe).
Radak (3, citing Shocher Tov): This is said in astonishment. All praise You, and You are silent in Tziyon?! "Kol Nasnu b'Veis Hashem k'Yom Mo'ed" (Eichah 2:7) - they said "Yadeinu Ramah v'Lo Hashem Pa'al Kol Zos", "Ei Elokeimo Tzur Chasayu Vo" (Devarim 32:27, 37). Also I am silent, like You - "Dom la'Shem v'Hischolel Lo" (above, 37:7).
Malbim: Praise is depicted as something tangible that stands silent in front of Hashem. Even though praise is speech, it stands silent in front of You. This itself is Your praise - You are elevated above all Brachah and praise!
Megilah 25a: A man said 'Hashem who is great, awesome, mighty, strong and vigorous.' R. Chanina said, did you finish His praises? If one has billions of gold coins, it denigrates him to say that he has silver.
Why did he say "Elokim b'Tziyon"?
Radak: The vows of Korbanos that the exiles make if You will return them to Tziyon, will be paid to You there in the Beis ha'Mikdash.
Radak (3): Most of the praise was in Tziyon, with songs, lyres and harps.
Why did he say "u'Lecha Yeshulam Neder"?
Radak: The vows of Korbanos that the exiles make if You will return them to Tziyon, will be paid to You there in the Beis ha'Mikdash.
Radak (3): Because their praise does not attain [what is proper for] You, they will pay their vows with Korbanos, to add to the praise.
Malbim: A vow is always an acceptance on condition that if the stipulation is fulfilled, he will pay the vow. To You there is no vow on condition, rather, it is paid immediately, for Your salvation will surely come; You are prepared for all who seek You, and the vow is paid immediately, even before the condition is fulfilled.
