And thou shalt kill the bullock before the Lord
That is, Moses is ordered to do it, who now officiated as a priest, "pro tempore", Aaron and his sons not being yet completely invested with that office, or thoroughly consecrated to it; of which consecration this sacrifice was a part, and therefore could not with propriety be concerned in killing their own sacrifice; for that purpose, Moses therefore did it, and he did it "before the Lord"; Jehovah the Son gave him those orders to do it before Jehovah the Father, in his presence, as an offering to him, and for his acceptance. And the ark, as Aben Ezra observes, was in the middle westward, and right against it was the altar of incense, and opposite that the altar of burnt offering:
by the door of the tabernacle of the congregation;
that is, as Jarchi interprets it, in the court of the tabernacle before the door; not by the door by which they entered in to the court of the tabernacle; but in the court before the door that leads in to the holy at some distance from which stood the altar of burnt offering, where this bullock was slain and sacrificed: all this may denote the public manner in which Christ, the antitype, suffered in the presence of the Lord, with his knowledge and will, and before the people of Israel.