Rashi: It was Rosh Hashanah ? Yom Teru'ah. Hashem commanded the Satan to bring the merit and liability of all creations. Ibn Ezra #1 - on Rosh Hashanah, all people come in front of the Shechinah for judgment.

Rashi (12): It was the day when they returned to eat in the house of the Bechor.

Ibn Ezra #2: It was the day when only Iyov was judged. I cannot explain this.

Ibn Ezra: It was the day when this occurred, like "va'Yhi ha'Yom v'Ya'avor Elisha."

Rashi (12): They are legion of Shamayim close to the Shechinah, like Bnei Bayis (His household).

Devar Eliyahu: They are judges who judge the world, like "Elohim Lo Sekalel."

Malbim: They are powers found in the entire creation that are His 'children' and handiwork.

Rashi: It is to argue with Him. This always refers to judgment ? "Nitzav Lariv Hashem" (Yeshayah 3:13).

Rashi (12): They stand around Him, like "l'Chol ha'Nitzavim Alav."

Devar Eliyahu: One who stands in front of one who sits, it is as if he stands over him. It says about Avraham "Sheloshah Anashim Nitzavim Alav." Lehisyatzev - they intended for His sake and honor, to judge and afflict those who oppose His will.

Malbim: They, and the entire world, exist only due to Him.

Rashi: It was to prosecute.

Ibn Ezra citing Rav Sadya Gaon: The Satan was a person who envied Iyov. "Kol Asher Lo b'Yadcha" (12) means to do as you want, like "ha'Yad Yo'av Itach" (Shmuel II, 14:19). "Es Nafsho Shemor" (below, 2:6) means guard your soul - do not seek to kill him. Angels do not envy ¹ !

Devar Eliyahu: Also the Satan intended l'Shem Shamayim, to judge those who rebel against Him.

Malbim: Also the Satan, the power of lack, the source of all evil, loss, sin and damage in the world, came among them. He did not come on his own - he has no root, just there must be lack among physical powers. He came to prosecute, and receive power to destroy and cause lack. All man's losses and sins are due to his physicality; all his attributes are due to his form.