Seeing as Bil'am had expressed regret at what he had done, why did Hashem not instruct him to go back?
Why did Hashem add the (otherwise superfluous) words "Lech Im ha'Anashim"?
Rashi: He instructed Bil'am to go with the men 1 because he was destined to suffer the same fate as them - to be destroyed from the world.
Seforno: He meant that Bil?am should go with the men only because they asked him to, not under his own steam, in order to curse Yisrael.
Even with the same intention as them (Refer to 22:22:2:11). Because, whereas until now, Hashem had attempted to protect Bil'am from self-destruction, He now withdrew that protection.
What are the implications of the word "ve'Efes ..."?
Rashi: It implies that, come what may, Bil'am will have to say whatever Hashem tells him. 1
Ramban #1: It implies, either that Bil'am was obligated to inform the emissaries of this condition, or that, Hashem was pardoning him for his sin, provided he remembered the condition. 2
Ramban #2: Because Bil'am wanted to curse Yisrael, and not to bless them under any circumstances, Hashem found it necessary to warn him, over and over again, to say whatever He told him to say. 3
Seforno: It implies that, in any event, Hashem was not worried that Bil?am might go against Hashem? wishes and curse Yisrael ? because He would only allow him to say what He put into his mouth.
Whether he likes it or not.
Ramban: To forestall any ideas that Bil'am may have that Hashem was allowing him to say whatever he was asked to say.
Ramban: And that explains why, the first thing Hashem told Balak (in Pasuk 38) was that he only had permission to come to him, but as far as speaking was concerned, he was only allowed to say what Hashem told him ? be it curses or blessings ? insinuating that if Balak did not agree, he would leave forthwith.
Why did the Mal'ach switch from "es ha'Davar asher Adaber ... oso Sa'aseh" (in Pasuk 20) to " ... oso Sedaber"?
Oznayim la'Torah (on Pasuk 38): When the Mal'ach instructed him " ... oso Sa'aseh", he thought that, as long as his actions conformed o Hashem's instructions, his speach - which was his tool of trade - was not bound by Hashm's instructions, so he went. But now that the Mal'ach decreed upon him "oso Sedaber", he realized that he could only say what Hashem told him to say 1 - and he immediately informed Balak (in Pasuk 38).
Interestingly, this did not deter him from trying again and again to get round the prohibition, and he only gave up at the beginning of chapter 24.
What are the implications of "Im Sarei Mo'av"?
Rashi: It implies that Bil'am accompanied the emissaries for the same motives as them 1 - that he was as happy to curse them as they were.
Refer to 22:22:2:11 & 22:22:1:1 and note.
Hashem already told him (in Pasuk 20) to do whatever He told him. Why did the angel repeat it?
Da'as Zekenim and Hadar Zekenim (on Pasuk 32): 'You will do whatever I tell you Bal Korchacha (against your will). If you go with your initial intentions, you will be killed by the sword!' He said this in order to frighten and confound him.