Why did Moshe need to call Aharon and his sons?
(9,1) “And it was (ויהי) on the eighth day that Moshe called to Aharon and to his sons, and to the elders of Yisrael.”
The reason why it was necessary for Moshe to call Aharon and his sons rather than come by themselves to ask about Hashem’s instructions can be explained according to the teaching of the Midrash, that whenever the Torah uses the expression ויהי it implies that something distressing occurred at that time. Here also the posuk says “ויהי on the eight day”, because on that day the two sons of Aharon died. And it says in Mishlei 14:10 “The heart knows the bitterness of one’s soul”, which means that even though a person himself does not know that something bad is going to happen, his mazal (what we call the sixth sense) knows. Therefore, since they sensed that that something bad was going to happen on that day, they did not want to approach to do their service, and therefore Moshe had to call them.
Similarly in a later posuk Moshe said to Aharon “approach the altar”, which implies that he did not wish to approach of his own accord. Rashi explained there in the name of the Midrash that the reason for this was because Aharon was reluctant to approach because he was ashamed due to his involvement with the golden calf, but we can also explain that he was reluctant to approach to do his service because his heart foretold that a bad thing was going to happen to him on that day.
Thus, although Aharon and his sons and the elders usually came by themselves before Moshe to learn from him Torah, since on that particular day a mishap was destined to happen through the performance of these mitzvos which would cause a loss to all of Yisrael (as it says later on “and all the house of Yisrael cried for the burning”) they did not go by themselves and needed to be called.
This is what the posuk is saying: “ויהי on the eighth day” - a distressing event was destined to happen on that day, and therefore “Moshe called to Aharon, and to his sons, and to the elders of Yisrael”. But in previous days they did not need to be called because they came by themselves.
Why, in this parsha, were Aharon and his sons not referred to by their title ‘Kohanim’?
(9,1) “And it was on the eighth day that Moshe called to Aharon, and to his sons, and to the elders of Yisrael.”
Another reason why the Torah uses the expression ויהי (which implies that something distressing occurred at that time) here is to teach us why it never says Aharon 'the Kohen' or the sons of Aharon 'the Kohanim' in this parsha. Now, the fact that we see that they are referred to simply as Aharon and his sons when the Torah is not discussing their priestly service is not remarkable, but when the Torah mentions them in connection with their priestly service, it usually describes them with their title - 'the Kohanim'. For example, in Vayikra 1:8 it says “and the sons of Aharon the Kohanim shall arrange…”, and Rashi explained there that the term comes to teach that they must conduct the priestly service dressed in their priestly garments. Here too, since the Torah is discussing their service, it should have called them ‘the Kohanim’.
But it is written in Koheles 8:8 “there is no ruling on the day of death”, and Chazal explain that for this reason Dovid was not referred to as ‘King Dovid’ when discussing his death, because on the day of death one is not a ruler. And since Chazal said on the posuk in Bamidbar 18:8 “Behold, I have given to you all the holy things of the children of Yisrael for distinction” - for greatness, like the kings eat, it is clear that the priesthood is considered like royalty, and thus the posuk “there is no ruling on the day of death” applies to them also.
Therefore, since on this day two of the sons of Aharon died - and in truth all of them were liable to be killed as the Midrash on this parsha teaches - for them this was a day of death, and so they were not referred to by their title of authority. And therefore the parsha opens with the words “ויהי on the eighth day” in order to hint that it would be a day on which there was to be trouble and distress, and therefore it was not fitting to refer to them as Kohanim in this parsha because there is no ruling on the day of death.
Why was a calf a suitable sin offering only for Aharon?
(9,2) “And he said to Aharon: Take for yourself a bull calf as a sin offering, and a ram as a burnt offering, unblemished, and bring them before Hashem.”
Rashi explained that the words "take for yourself a calf" was to inform Aharon that Hashem was granting him atonement with this calf for the incident of the golden calf which he had made. But it cannot be that Rashi is coming to tell us the reason why Hashem specifically chose a calf for his sin offering, because how then would he explain all the other offerings of Aharon and the congregation - why was such-and-such an animal brought for a sin offering, this one for a burnt offering, and this one for a peace offering? Perforce, we have to say that we cannot give reasons for Hashem’s decrees. If so, why did Rashi write here that the command to "take for yourself a calf" was to inform Aharon that he was being granted atonement with this calf?
But we can explain Rashi after we understand the gemora in Yoma 3b on our posuk, “take for yourself”. One opinion holds that this phrase means that Aharon should pay for the offering out of his own pocket, but another opinion holds that it is bought from the public coffers. If so, what does the phrase "take for yourself" mean according to this latter opinion? The gemora answers that the Torah is implying that Hashem is saying to Aharon: It is yours that I desire, and I do not desire that of the public. What does this gemora mean?
The Midrash on parshas Beshalach teaches on the posuk in Shemos 15:1 “Then sang Moshe”, that with the word then Moshe sinned before Hashem when he said “and from then when I came to Pharaoh to speak in Your name, You did evil to this people” (Shemos 5:23), and therefore with the word then Moshe praised Hashem, as it says, “then sang Moshe”, because tzaddikim rectify their sin in the same way in which they sin. But how does using thesame language as that of the sin help to rectify the sin?
It seems to me that if a person actually does a real sin it is impossible to rectify his sin with that with which he sinned, because the rule is that ‘an accuser cannot become a defender’. For this reason it is forbidden for the Kohen Gadol to enter the Holy of Holies on Yom Kippur wearing golden vestments, because the accuser (gold, used for the sin of the golden calf) cannot become a defender. If so, how could Moshe Rabbeinu rectify his sin using the language with which he had sinned, and how could Aharon achieve atonement with the calf that he brought?
The answer is that there are sins which if an ordinary person would do them are not actually sins at all, but if a Tzaddik does them because of his great spiritual level they would be considered sins. As Chazal taught on the posuk in Tehillim 50:3 “and around Him it storms furiously” - that Hashem is very exacting with tzaddikim. Therefore, for a sin such as this the rule that the accuser cannot become a defender does not apply, because it is not really a sin. And even if we would consider it to be a sin because of the level of the Tzaddik, how could there be any accuser? To make it an accuser, we would to have to mention the great righteousness of the Tzaddik which made this a sin. If so, his accuser would itself be his defender!
Therefore, the Midrash says that tzaddikim, specifically, rectify their sin in the manner in which they sinned, because the 'superiority' of their sin allows it to be thus rectified. And this also shows that it is not an actual sin, because if it was, it would not help to rectify it in this way.
This is what our posuk is saying: “Take for yourself a bull calf” - from you I desire atonement with a calf, but I do not desire this from the public, because for them atonement with a calf would not suffice. On the contrary, for them the calf would be detrimental because an accuser cannot become a defender.