Why does it say "Barchu Hashem Mal'achav"?
Radak (19): All should bless Hashem, for all are under His authority. The verse begins with the angels (upper beings), and concludes with lower beings.
Radak: They are a higher level than all [other] created beings. All motion of the spheres and stars is via them.
Radak citing Shocher Tov: Since the next verse says "Barchu Hashem Kol Tzeva'av", we must say that our verse addresses lower beings. We find that they are called Mal'achim - "va'Yishlach Mal'ach va'Yotzi'enu mi'Mitzrayim" (Bamidbar 20:16). This was Moshe. Likewise, "va'Yomer Chagai Mal'ach Hashem" (Chagai 1:13). Some say that "va'Ya'al Mal'ach Hashem Min ha'Gilgal" (Shoftim 2:1) refers to Pinchas, and some say that "u'Mar'ehu k'Mal'ach ha'Elokim Nora Me'od" (ibid., 13:6) refers to him. This shows that Nevi'im are called Mal'achim 1 .
Ma'alos ha'Torah (DH Od Sham, citing the Zohar): Those who engage in Torah are called Mal'achim.
Malbim: The Mizmor concludes with mentioning His conduct in three worlds that He created. (a) The Brachah and influence that He puts on the world of angels; they bless Him for this. They are called Mal'achav, for a Mal'ach goes on an honored mission, only sometimes. Also refer to 103:21:1:2, 103:22:1:3.
According to the opinion that Pinchas is Eliyahu, Mal'ach ha'Bris, we cannot learn from Pinchas to other Nevi'im. (PF)
Why are they called "Giborei Cho'ach"?
Radak citing Ibn Ezra: No created being can stand against them. The angel that came [to fight] against Yakov was commanded 1 .
Malbim: They are ready to do Hashem's mission, to override nature when needed. This refers to angels above the Kisei (Ma'arachah) - "Serafim Omedim mi'Ma'al Lo" (Yeshayah 6:2). They do not have fixed laws. Hashem conducts miraculously only sometimes, when needed.
I.e. he was commanded to fight Yakov and not defeat him, so that Yakov would not fear Esav (Radak Bereishis 32:25). However, if not for the command, Yakov (or any other human) could not stand up against an angel. (PF)
What do we learn from "[Giborei Cho'ach] Osei Davaro"?
Shabbos 88a: When Yisrael put 'Na'aseh' before 'Nishma', a Bas Kol said 'who revealed to My children this secret that the angels use?' First Osei (they accept to do) His word, and afterwards they hear it.
Radak: They do everything according to His commands and words.
Radak citing Ibn Ezra: Decrees that descend from Shamayim come via them, like the matter of [wiping out the camp of] Sancheriv. Moshe said "va'Yishlach Mal'ach" (Bamidbar 20:16), and it says "Mal'ach Panav Hoshi'am" (Yeshayah 63:9).
Mesilas Yesharim (Perek 6): Angels are praised for the Midah of Zerizus, to invigorate themselves and overpower to do commands.
Why does it say "Lishmo'a b'Kol Davaro"?
Radak: They always do what He commands them, and they are ready to hear what He will command.
Radak citing Ibn Ezra: They are not like people, who hope to get reward from Hashem for doing His word. Their reward, pleasure and glory is hearing His word!
Radak, based on Shocher Tov #1: It says so after "Osei Davaro"; this refers to Yisrael, who put 'Na'aseh' before 'Nishma.'
Shocher Tov #2: This refers to people who observe Shemitah. Normally, a person does a Mitzvah for a short time, or a day. Yisrael observe Shemitah for a year!
Shocher Tov #3: This refers to Moshe, who was able to hear Hashem's voice. Angels cannot - "va'Shem Nasan Kolo Lifnei Cheilo Ki Rav Me'od Machanehu" (Yo'el 2:11). "Machanehu" is angels - "Machaneh Elokim Zeh" (Bereishis 32:3).
Malbim: They go only when they get an explicit command from their Creator.
