What are the connotations off "Vayitav be'Einav"?
Rashi and Targum Yonasan: Moshe admitted that Aharon was right and in spite of the shame involved, 1 he admiited that he had learned it and forgot it (and even issued a proclamtion in the camp to that effect ? Targum Yonasan) and did not deny having learned it.
Seforno: He rejoiced over his brother Aharon and his son's straight line of thinking, that they got it right and taught him the truth.
Targum Yonasan: He was pleased with Aharon's reply, and announced in the camp that he had forgotten the Halachah and that Aharon his brother had reminded him.
Oznayim la'Torah: Refer to 10;19:5;6. Aharon's humility found favor in the eyes of the humblest man.
And that he forgot it (Rashi).
What caused Moshe to err?
Rashi (citing Vayikra Rabah): Because he was angry with Elazar and Isamar, he forgot (and anger causes a person to make mistakes - Rashi, in Mattos Bamidbar, 31:21). 1
Hadar Zekenim (in Sh'mos 16:20): The same occurred in two other places, 1. With the people who left over the Manna - when he subsequently forgot to tell Yisrael that they will get extra on Friday for Shabbos (ibid); 2. With the soldiers who failed to kill the daughters of Midyan - when he subsequently forgot to tell the people to KAsher the Keilim taken from Midyan (Mattos Bamidbar, 31:21).
QUESTIONS ON RASHI
Rashi writes that because Moshe was angry, he forgot. Seeing as Aharon and his sons had acted croccectly was did he become angry?
Rashash (in Vayikra Rabah 13:1): This is like the opinion (in Zevachim 101a) that it was burned due to Tum'ah; otherwise, they could have eaten it at night, after the Din of Aninus terminated. Moshe, unaware of the Tum'ah, was angry why they burned it, and did not leave it to eat at night. He thought that, on account of their grief they were negligent and allowed it to became Tamei. And because he was angry, he forgot that they may not eat it during the day, and asked why they did not eat it.
Toras Moshe (in Pasuk 19): They should have eaten a k'Zayis immediately after burning the Emurim. 1
Toras Moshe: Aharon answered "ha'Yitev be'Einei Hashem" - the Zakai atones for the Chayav. Until the decree against me (that my sons die) was [partially] fulfilled, I was not Zakai; it would not have atoned properly. Hashem caused us not to eat it promptly, forecause Yisrael did not deserve the full Kaparah. And Moshe accepted the answer.
Rashi writes that Moshe was not ashamed to say 'I did not hear.' What is the Chidush, bearing in mind the Mishnah in Avos 5:7 - that tThis is a Midah of Chachamim?
Riva and Rosh (in Pasuk 19 - both citing Zevachim 101a): Moshe did not say, due to shame, ' I did not hear', but 'I heard, and I forgot.' 1 This is the intention of Rashi, even if it is not explicit in Rashi's words.
Toras Moshe: Moshe did not hear explicitly, but he was shown what every Chacham will be Mechadesh, He himself was Mechadesh the law, but Aharon went deeper to distinguish Kodshei Doros from Kodshei Sha'ah. Moshe admitted that he did not fully understand his own Chidush; he was not concerned for lest people say that one cannot rely on him. "It was good in his eyes" to share with Yisrael Pilpul (deep investigation) which was given to him alone.
Shir Ma'on: The Chidush is that he recognized that Aharon was right - "Toras Emes Haysah be'Fihu"(Mal'achi 2:6) - and admitted, and he was happy about this.
Moshav Zekenim: In Shabbos (119b), we find that it is a greater shame to say 'I never learned' than 'I learned and forgot'! There, one should have learned from a Rebbi. Here, if Hashem did not tell Moshe, he is not to blame for not knowing! Divrei David - there, to say 'I never learned any Torah' is a great shame. Here, to say 'I never learned this law' is not a big shame. Alternatively, here, to say 'I did not hear explicitly. I reasoned this way, and Aharon convinced me to retract' is not shameful. This does not apply there.