Charles Ellicott Commentary Leviticus 4:7

"And the priest shall put of the blood upon the horns of the altar of sweet incense before Jehovah, which is in the tent of meeting; and all the blood of the bullock shall he pour out at the base of the altar of burnt-offering, which is at the door of the tent of meeting." — Leviticus 4:7 (ASV)

And the priest shall put. —That is, the high priest. With his finger, so dipped into it, he was to put some of the blood on each of the four horns of the golden altar on which the incense was offered.

This process, too, was peculiar to the sacrifice of the sin offering. The altar was placed in the holy place before the veil which separated off the Holy of Holies (Exodus 30:1–6). According to the practice that prevailed in the time of Christ, the priest began by putting the blood first on the north-east horn, then on the north-west, then on the south-west, and lastly, on the south-east horn. He dipped his finger in the blood of the bowl at the sprinkling of each horn, and wiped his finger on the edge of the bowl between the separate sprinklings, as the blood that remained on his finger from one horn was not deemed fit to be put on the other.

And shall pour all the blood. —That is, all the remaining blood. The bulk of the blood that remained, after expending the small quantity on the horns of the incense altar inside the sanctuary, the priest poured out at the bottom of the altar of burnt offering, which stood outside the holy place. At the time of the Second Temple, there were at the southwest horn of this altar two holes, like two nostrils, through which the blood ran into a drain conveying it into the Brook Kidron.