What do we learn from "va'Omar Aleihem"?
Rashi: I said to the remaining kings of Yehudah.
Radak: [They will know that] it was Devar Hashem that He told to them via the Nevi'im.
What is the meaning of "Im Tov b'Eineichem Havu Sechari"?
Rashi: Fulfill My Mitzvos, all this will be My 'wage' for all the good that I gave to you, like they pay a shepherd, and I will return to tend you.
Radak: Since I tend you, give My wage, i.e. Teshuvah and good deeds.
Radak citing Targum Yonasan: If it is proper in your eyes, do My will.
Malbim: This is a Mashal, as if Hashem requested wages for guarding them, lest the Bayis be destroyed and enemies consume them. Hashem wanted that they will have merit to advocate for them in front of Him.
What do we learn from "v'Im Lo Chadalu"?
Rashi: If not (you will not fulfill My Mitzvos), also I will not benefit you. So Hashem told Yechezkel "ha'Shome'a Yishma veha'Chadel Yechdal" (3:27).
Radak: This is like He told Yechezkel "Im Yishme'u v'Im Yechdalu" (2:5).
Radak citing Targum Yonasan: If you will refrain [from doing My will], a small number will [repent].
Malbim: If you will not give [My wage], you will not have merit, and you will cease to be a nation.
What is the significance of weighing 30 Shekalim for His wage?
Targum Yonasan: A small number of men did My will. Rashi ? e.g. ha'Charash veha'Masger, Daniel, Chananyah, Misha'el, Azaryah and Yechezkel. I cannot explain Sheloshim Kasef. Kesef is an expression of desired. Chachamim said so ("Kesef'" refers to Tzadikim ? Chulin 92a). They proved this from "Tzeror ha'Kesef Lakach b'Yado" (Mishlei 7:20).
Chulin 92a #1: There are 30 righteous Nochrim on whom the rest of the world stands.
Chulin 92a #2: These are the 30 Mitzvos that the Nochrim accepted on themselves 1 . They keep only three.
Rashi citing Tanchuma Miketz 6: Hashem promised Avraham that no generation will have less than 30 Tzadikim. This is the Gematriya of "Ko Yihyeh Zar'echa" (Bereishis 15:5). Malbim ? the Tzadikim were Moser Nefesh for Kidush Hashem rewarded them ? He returned to tend His flock.
Radak: There were 30 Tzadikim in the days of these three shepherds. We find among them Daniel, Chananyah, Misha'el, Azaryah, Yirmeyahu, Yechezkel and Tzefanyah. Surely there were more, even if they were not mentioned ? "Nasenu Es Nivlas Avadecha Ma'achal l'Of ha'Shamayim Besar Chasidecha l'Chayso Aretz" (Tehilim 79:2).
Radak (14, citing his father): They repented, but it was complete only for the 30 days that they mourned over the Kohen Gadol.
Radak (14 citing R. Avraham ha'Levi): This hints to 30 years that kings of Chesed ruled ? Matisyahu, who is called Chashmona'i, ruled one year; his son Yehudah ruled six years, his son Yonason six years, and his son Shimon 18 years. These add to 31 ? if some months were missing, they are 30 in all.
Malbim: Refer to 11:13:1:5.
Maharav Ransborg (92a) gives references discussing the 30 Mitzvos.