Lévitique 1:5

And the slayer shall kill the ox at the place of slaughter before the Lord, and the sons of Aharon the priest shall bring the blood in vessels, and sprinkle the blood which is in the basins round about the altar that is at the door of the tabernacle of ordinance.

before God The same phrase is used apropos the sheep burnt offering [:11], where the subsequent phrase “the northern side of the Altar” localizes the slaughter directly opposite the Table.

One kohen will slaughter [singular] the animal, but many will throw [plural] the blood , as it is written: “Aaron’s sons handed him the blood” [9:12].

the one at the entrance of the Tent i.e., not the Incense Altar.

AND HE SHALL SLAUGHTER THE BULL BEFORE THE ETERNAL. AND THE PRIESTS, AARON’S SONS, SHALL OFFER THE BLOOD. “All acts from receiving [the blood in a vessel] onwards are the duty of the priests. This teaches that the slaughtering [of the offering] is valid if performed by a zar (non-priest). ‘V’hikrivu’ (and they shall offer …) — this refers to ‘receiving’ [the blood], and the sense thereof is the bringing [of the blood to the altar]. Thus we learn that both of them [receiving the blood and bringing it to the altar], are to be done by Aaron’s sons.” This is Rashi’s language.
But it is not correct. has a primary meaning of “receiving” the blood in a vessel, which is the first process after the “slaughtering” mentioned immediately before in the verse, and a subsidiary meaning [from the root ‘karav’, to bring near] of “bringing” it to the altar. To this Ramban objects that ‘v’hikrivu’ is not derived from the root ‘karav’, implying bringing near, and hence cannot sustain the interpretation of “bringing it near” the altar even as a subsidiary meaning. Rather, it is associated with the word ‘korban’ (offering), and has only one meaning, that of “receiving” the blood, which is the first stage in offering. If so, whence do we know that bringing it near the altar may also be done only by priests [and is invalid if done by a non-priest]? To this Ramban replies that it is a logical deduction [“if receiving the blood may only be done by priests, it follows ‘all the more’ that bringing it to the altar, which is a later stage in its offering, has this requirement”]. A careful reading of Rashi and Ramban clearly indicates this interpretation. Instead, the Midrash of our Rabbis states: 4:4. “V’hikrivu — this is the receiving of the blood.” For the term v’hikrivu does not mean the bringing of the blood near to the altar, namely the holachah (carrying of it). Instead, v’hikrivu is an expression similar to the word korban (offering) and it signifies receiving [of the blood in a vessel] and sprinkling it upon the altar. Thus He mentioned bringing it [to the door of the Tent of Meeting], laying hands on it, and slaughtering it with reference to the owner of the offering, and after the slaughtering He immediately mentioned the sons of Aaron. It accordingly follows that receiving the blood is in itself a duty to be performed by the priests, and may only be done by a qualified priest and with vessels dedicated to the Temple Service; and [it follows] all the more that bringing it to the altar and sprinkling it [can be done only by a qualified priest]. Moreover, even carrying of the limbs to the ramp [leading to the altar] is invalid if done by a non-priest, for so the Rabbis interpreted: “And the priest shall offer it all, and cause it to ascend in fumes upon the altar — this refers to carrying of the limbs to the ramp.” If so, carrying the blood to the altar also may be done only by a priest with all the conditions of priesthood.

והקריבו, the term includes catching the blood after slaughtering the sacrifice, bringing it to the altar and performing the sprinkling of it on the appropriate parts of the altar. Our sages also explain the word והקריבו in this sense. (compare Zevachim 7)

אשר פתח אהל מועד, not the golden altar which was inside the Tabernacle.

ושחט, “he will slaughter, etc.” the Torah used the singular mode as ordinarily one person performs that act. On the other hand, when describing the steps following the act of slaughtering, the Torah uses the plural mode, as a number of priests are usually involved in that.

את בן הבקר, “the bullock;” the expression: בן הבקר implies that the animal is male and young, as it is forbidden to offer diseased or overage animals.(Compare Malachi 1,8 הקריבהו נא לפחתך, “just offer it to your governor!”) [The prophet reminds people that they would not dare offer a governor something less than first rate as he becomes aware of it immediately and will feel insulted. Ed.]

בני אהרן, the Torah does not mean that other priests are not qualified, but used the sons of Aaron as examples of priests in their prime. This corresponds to what the Talmud stated in tractate Chulin folio 24, according to which priests have to retire from active service when their hands and feet have become red as a sign of weakness.