What is the meaning of "Kohanecha Yilbeshu Tzedek"?
Radak: Kohanim will serve wearing Bigdei Kehunah, which are Bigdei Tzedek. Malbim - until now they did not wear Bigdei Kehunah 1 ; now they will wear Tzedek. The design of the garments showed Tzedek and Midos Tovos that clothe the Nefesh, like Chazal said.
How can he say so?! The Torah commands about Bigdei Kehunah, and a Kohen who serves without them is like a Zar, and disqualifies the Avodah (Zevachim 17b)! Perhaps he explains 'Ein Minchah b'Vamah v'Chihun u'Vigdei Shares' (ibid., 113a) to mean even a Bamah Gedolah, unlike Rashi (113a), Tosfos (119b) and the Rambam (Zevachim 14:10). (PF)
Who are "Chasidecha"?
Radak: They are the Leviyim 1 ; they will sing in front of You [Malbim - when Korbanos are offered].
Radak (16): This is like "l'Ish Chasidecha" (Devarim 33:8, in the Brachah to Levi. That refers to the Kohen Gadol ("Tum'echa v'Urecha"). What is the source that all Leviyim are called Chasidim? - PF)