Why will the angel not forgive those who do not obey him?
Rashi: Because a. He is not accustomed to sin, since he is an angel, who does not sin 1 , and b. because, as a Shali'ach of Hashem, he is obligated to carry out Hashem's command, in which case he has no mandate to pardon those who sin. 2
Rashbam: Because He speaks in Hashem's Name. 3
Da'as Zekenim: Because My name is in his, rebellion against him is like rebellion against Me; only I can pardon this.
Why does the Torah switch from the singular ("Al Tamer bo") to the plural ("Ki Lo Yisa le'Fish'achem")?
Seforno: To teach us that, even when one person sins, the entire community suffers 1
As we find by Achan
What are the connotations of "Ki Sh'mi be'Kirbo"?
Rashi #1 and Ramban #1: It is because Hashem's Name is contained within the angel that Hashem will send, that one should take care not to disobey him. 1
Rashi #2: This refers to the angel Matatron, whose Gematriyah (314) is equal to that of Hashem's Name, Shakai.
Ramban #2 (citing Kabalah): This is the Redeeming Angel, 2 which, according the Gemara in Sanhedrin, 38b) is synonymous with Matatron referred to in Vay'chi, and whom he discussed at length in Bereishis 46:1. 3
Ramban #3, Rashbam, Targum Onkelos and Targum Yonasan: Do not disobey him because he speaks in My Name. 4
Hadar Zekenim: Hashem's name is a part of the name of every angel.
Rosh: Shmi is an acronym for Sonei Matanos Yichyeh. Do not think that you will sin and give to him bribes to pardon you!
Moshav Zekenim: He has like tablets opposite his heart, and Hashem's name is written on them - "Shem Hashem Ba mi'Merchak" (Yeshayah 30:27).
And the one who disobeys him therefore deserves to be destroyed via the Midas ha'Din (Ramban).
Which is synonymous with the Shechinah (Kevayachol), and whom Moshe replaced during his lifetime (See Sh'mos 7:11), and who appeared to Yehoshua prior to the conquest of Cana'an. The Ramban goes on to name him as the angel Gavriel. In any case, this is not the angel that Hashem said He would send, and Moshe succeeded in preventing this through his Tefilos (See Ramban and refer to 23:21:1:1**).
Because his voice is synonymous with the Voice of Hashem (Ramban).
What was the identity of thje Mal'ach that Hashem planned to send after the Chyet ha'Eigel?
QUESTIONS ON RASHI
Rashi writes that "Shmi b'Kirbo" refers to Matatron, whose Gematriyah (314) equal that of, Shakai. Many names have this Gematriya!