כִּֽי־פְ֭שָׁעַי אֲנִ֣י אֵדָ֑ע וְחַטָּאתִ֖י נֶגְדִּ֣י תָמִֽיד׃
Car je reconnais mes fautes, et mon péché est sans cesse sous mes regards.
Ramban
DRAW NEAR UNTO THE ALTAR. 8. AND AARON DREW NEAR UNTO THE ALTAR AND SLEW THE CALF. It seems to me in accordance with the plain meaning of Scripture that Moses said to Aaron: “Draw near to the north side of the altar and offer there the sin-offering and the burnt-offering, for they are to be slaughtered on the north side of the altar.”25Above, 1:11; 6:18. Moses, however, said it briefly since Aaron already knew [that these offerings were to be slaughtered on the north side of the altar].
Our Rabbis in the Torath Kohanim were, however, prompted by [the use of] these expressions to draw a parable [and to say]:26Torath Kohanim, beginning of Shemini 8. The Rabbis were prompted by the use of the phrase “draw near,” which Ramban explained to mean “draw near to the north side of the altar.” “To what can this be compared? To a human king who married a woman, who in her shyness [did not dare to enter] before him. Her sister then approached her, saying, ‘My sister, why did you enter this matter? Was it not in order that you serve the king? Embolden yourself and go in to serve the king!’ Similarly did Moses say to Aaron: ‘My brother! Why were you chosen to be the High Priest? Was it not so that you minister before G-d? Embolden yourself and come and do your priestly activities.’ Some Rabbis say that Aaron saw the [horned] altar in the form of the bull [which — as stated in Psalms 106: 20 — Israel had worshipped], and he was frightened by it. Then Moses came near and said to him, ‘My brother, Aaron, do not be afraid of that which you fear. Embolden yourself and come near it.’ This is why he said, draw near unto the altar, and [Aaron] drew near unto the altar — with zeal.” The reason for this [apparition which Aaron saw in the altar] was that since Aaron was the holy one of the Eternal,27Psalms 106:16. having no sin on his soul except for the incident of the golden calf, therefore that sin was firmly fixed in his mind, something like that which is said, and my sin is ever before me.28Ibid., 51:5. It thus appeared to him as if the form of the calf was there [in the altar] preventing his [attaining] atonement [through the offerings he was to bring]. That is why Moses said to him, “Embolden yourself so that you should not be of such humble spirit,” for G-d has already accepted his works.29See Ecclesiastes 9:7. Other scholars explain that it was Satan who showed him this apparition, just as they have said there in the Torath Kohanim:30Torath Kohanim, beginning of Shemini 3. “My brother Aaron, although G-d has agreed to grant atonement for your sin, you must nonetheless close the mouth of Satan [through your offerings], lest he accuse you when you enter the Sanctuary etc.” And the expression, and make atonement for thyself, and for the people means as follows: “draw near unto the altar to bring all the offerings, and offer first thy sin-offering, and thy burnt-offering, and make atonement for thyself first with thy offerings, and for the people afterwards, through bringing their offering and atoning for them by means thereof.” Thus Moses taught Aaron that the guiltless should come and effect atonement for those who are guilty.31Yoma 43 b.
Our Rabbis in the Torath Kohanim were, however, prompted by [the use of] these expressions to draw a parable [and to say]:26Torath Kohanim, beginning of Shemini 8. The Rabbis were prompted by the use of the phrase “draw near,” which Ramban explained to mean “draw near to the north side of the altar.” “To what can this be compared? To a human king who married a woman, who in her shyness [did not dare to enter] before him. Her sister then approached her, saying, ‘My sister, why did you enter this matter? Was it not in order that you serve the king? Embolden yourself and go in to serve the king!’ Similarly did Moses say to Aaron: ‘My brother! Why were you chosen to be the High Priest? Was it not so that you minister before G-d? Embolden yourself and come and do your priestly activities.’ Some Rabbis say that Aaron saw the [horned] altar in the form of the bull [which — as stated in Psalms 106: 20 — Israel had worshipped], and he was frightened by it. Then Moses came near and said to him, ‘My brother, Aaron, do not be afraid of that which you fear. Embolden yourself and come near it.’ This is why he said, draw near unto the altar, and [Aaron] drew near unto the altar — with zeal.” The reason for this [apparition which Aaron saw in the altar] was that since Aaron was the holy one of the Eternal,27Psalms 106:16. having no sin on his soul except for the incident of the golden calf, therefore that sin was firmly fixed in his mind, something like that which is said, and my sin is ever before me.28Ibid., 51:5. It thus appeared to him as if the form of the calf was there [in the altar] preventing his [attaining] atonement [through the offerings he was to bring]. That is why Moses said to him, “Embolden yourself so that you should not be of such humble spirit,” for G-d has already accepted his works.29See Ecclesiastes 9:7. Other scholars explain that it was Satan who showed him this apparition, just as they have said there in the Torath Kohanim:30Torath Kohanim, beginning of Shemini 3. “My brother Aaron, although G-d has agreed to grant atonement for your sin, you must nonetheless close the mouth of Satan [through your offerings], lest he accuse you when you enter the Sanctuary etc.” And the expression, and make atonement for thyself, and for the people means as follows: “draw near unto the altar to bring all the offerings, and offer first thy sin-offering, and thy burnt-offering, and make atonement for thyself first with thy offerings, and for the people afterwards, through bringing their offering and atoning for them by means thereof.” Thus Moses taught Aaron that the guiltless should come and effect atonement for those who are guilty.31Yoma 43 b.
Rabbeinu Bahya
According to Nachmanides we must not misunderstand this Midrash as meaning that Aaron saw (a non-existent) figure of a bull on the Altar. The Midrash means that the only sin which Aaron had been guilty of was the making of the golden calf (bull). This is why the sin was constantly in his thoughts. It was just like when David said in Psalms 51,5 concerning his own sin: “my sin is constantly present in my mind.” Aaron looked at the Altar as if it were the personification of his sin, reminding him of it even more visibly. He was afraid that such thoughts would interfere with his ability to offer sacrifices from here on in. This is why Moses had to put his mind at rest telling him that he did not have anything to worry about as his part in that sin had already been forgiven.
Tur HaArokh
ויקרב אהרן אל המזבח וישחט, “Aaron approached the altar and slaughtered;” Nachmanides writes that in his personal view, the plain meaning of the words קרב אל המזבח is that Aaron is to approach the north side of the altar where he is to perform the procedures involving the sin offering and the burnt offering, seeing these two types of offerings need to be slaughtered on the north side of the altar. (Zevachim chapter 5) The catching of the blood of these offerings must also be carried out on the north side of the altar in the appropriate vessels. Moses recorded this in abbreviated form as Aaron was already familiar with the procedure. According to a Midrash, seeing that Aaron was a קדוש ה', someone sanctified by Hashem, his life having been stained only by one marginal sin, his involvement in the sin of the golden calf, this sin was something which preyed on his mind constantly, similar to David’s remark וחטאתי נגדי תמיד, “and I am constantly conscious of my sin against You.“ (Psalms 51, 5) He felt that the image of the golden calf constantly intruded upon his imagination and interfered with the proper concentration required when presenting sacrifices on behalf of others. This is why Moses tried to restore his mental equilibrium by telling him not to be depressed, that G’d had already forgiven his involvement in that sin. Some commentators think that it had been Satan that had shown Aaron these images of the golden calf, and that Moses told Aaron that in spite of he fact that as far as G’d was concerned, his sin had been forgiven, he also had to do something to shut up Satan so that the latter would not be able to upset him at the crucial time when he would perform sacrificial duties. This is the approach taken to our verse by Torat Kohanim.