If Bil?am did not know that the angel was standing in front of him, what did he mean when he said ?Chatasi??
Seforno: He meant that his stubbornness prevented him from realizing that min ha?Shamayim, they were trying to stop him from going.
After having admitted here that he did not even know when an angel was standing in front of him, how can Bil'am later (in 24:16) describe himself as "Yode'a Da'as Elyon"?
Rashi #1: His admission here does indeed negate his boastful claim that he knew Hashem's Mind.
Rashi #2 and Targum Yonasan: Refer to 24:16:1:1.
Hadar Zekenim: Refer to 24:16:1:4.
Why did Bil'am add the words "Im Ra "be'Einecha"?
Rashi: His statement insinuated an accusation against Hashem - Having granted him permission to go with Balak's dignitaries, why did He send an angel to negate it? 1 Be that as it may, he conceded that, if it is really bad in the Eyes of Hashem, he would have no choice but to retract.
Seforno: What he meant was that if it is bad in the eyes of the angel - who is presumably a defense counsel of Yisrael, he will have to go back, so as not to act against his wishes - despite the fact that Hashem had granted him permission to go.
Rashi: Just as He did by the Akeidah, when, after instructing Avraham to sacrifice his son, He sent an angel to negate His initial instructions.
Why did Bil'am not claim that he did not sin, since he did not know that the angel was blocking his path'?
Moshav Zekenim: From here we learn that a Ben Noach is warned, because he should have learned - Bil'am should have realized that the ass was veering off the path for a reason. Presumably, it saw an angel; and seeing as Hashem and the angel were upset that I am going, he ought to have returned.