Why does it say "v'Chafrah ha'Levanah u'Voshah ha'Chamah"?
Rashi citing Targum Yonasan: Those who serve the moon will be shamed, and those who serve the sun will be humbled.
Radak: The world will become dark on the Nochrim due to the many afflictions. This will be in the war of Gog and Magog.
Malbim: People will no longer attribute divinity to the sun and moon, for they will recognize that Hashem is the First cause, and He is the First and Last influence. He oversees in Shamayim above and on the land below. The idolaters used to ascribe divine power to the sun. It influences light on the moon and stars. They used to honor also the moon, for they thought that it receives influence from the sun and influences on the lower world and rules on it. Then it will be shamed, for they will know that the supreme honor will not be put on it, rather, on Hashem's Chachamim and Nevi'im. They will be Neged Hashem, like the moon is Neged the sun. They will receive His light, and from them influence will descend to the land and those who live on it.
It says "v'Chafrah ha'Levanah u'Voshah ha'Chamah" (they will not illuminate much), and it says "v'Hayah Ohr ha'Levanah k'Ohr ha'Chamah... Shiv'asayim k'Ohr Shiv'as ha'Yamim" (30:26)!
Sanhedrin 91b #1: In Yemos ha'Mashi'ach they will be bright. In the world to come they will appear dim (due to the great radiance of Tzadikim).
Sanhedrin 91b #2: Both refer to the world to come 1 . In the place of Tzadikim they will be bright, in the place of the Shechinah they will appear dim.
So the Gemara answers for Shmuel, who says that the only difference between this world and Yemos ha'Mashi'ach is that the kingdoms will cease to rule over Yisrael.
Why does it say "Ki Malach Hashem Tzevakos b'Har Tziyon uvi'Yrushalayim"?
Radak: Then, Hashem's kingship will be seen in Har Tziyon and Yerushalayim. There, they will camp against the city, and conquer half of it (Zecharyah 14:2). Hashem will go out to fight with those Goyim. Then, all remaining Goyim will recognize that kingship is of Hashem.
Malbim: This is why the sun will be ashamed - the light of His kingship will be in place of the sun's light.
Why does it say "v'Neged Zekenav Kavod"?
Rashi: This is like it says above "Yihyeh Tzemach Hashem li'Tzvi ul'Chavod; v'Hayah ha'Nish'ar b'Tziyon..." (4:2-3). They are the Zekenim mentioned here.
Mesilas Yesharim (Perek 22): Honor is attributed to Tzadikim, for it dwells on them and does not depart from them.
Malbim: This is why the moon will be ashamed - the Zekenim will receive the light of His honor in place of the moon.
