(10) Aaron shall make an atonement upon the horns of it once in a year.--This passage seems to determine the sense of Leviticus 16:18, where some have supposed that "the altar that is before the Lord" is the brazen altar. Once in the year, on the great day of atonement, the high priest, after entering within the vail and sprinkling the blood of the offerings upon the mercy seat (Leviticus 16:14-15), was to "go out unto the altar that was before the Lord, and put of the blood of the bullock, and of the blood of the goat, upon the horns of the altar round about, and sprinkle of the blood upon it with his finger seven times," and so "cleanse it, and hallow it," and "make an atonement for it" (Leviticus 16:18-19).

Verse 10. - Aaron shall make an atonement upon the horns of it once in the year. Once in the year, on the great day of atonement - the tenth day of the seventh month - the high priest, after burning incense within the veil, and sprinkling the blood of a bullock and a ram towards the mercy seat, was to take of the blood, and put it on the horns of the altar of incense "to make an atonement for it - to cleanse it and hallow it from the uncleanness of the children of Israel" (Leviticus 16:18, 19). This was not making it an altar of expiation, but merely expiating it. There was, however, another use for the altar, where it seems to have served for an altar of expiation. When the high priest had sinned in his official character, and offered a sin-offering for his cleansing (Leviticus 4:3-12), or when the whole congregation had committed an offence through inadvertence, and did the same (ib, 13-21), the high priest was to put of the blood of the sacrifice on the horns of the altar of incense, "for the expiation of his own sin and the sin of the people" (Keil). In these two cases, the altar of incense served the purpose of the altar of burnt-offering, on which was put the blood of private sin-offerings (ib, 22-35). It is most holy. There seems to be sufficient reason for considering the altar of incense as, next to the ark and mercy seat, the most sacred object in the furniture of the tabernacle. This precedence indicates the extreme value which God sets upon prayer.

CHAPTER 30:11-16

30:1-10 The altar of incense represented the Son of God in his human nature, and the incense burned thereon typified his pleading for his people. The continual intercession of Christ was represented by the daily burning of incense thereon, morning and evening. Once every year the blood of the atonement was to be applied to it, denoting that the intercession of Christ has all its virtue from his sufferings on earth, and that we need no other sacrifice or intercessor but Christ alone.And Aaron shall make an atonement upon the horns of it once in a year,.... On the day of atonement, as the Targum of Jonathan, and so Jarchi and Aben Ezra explain it; and the atonement here referred to seems to be an atonement for the altar itself, see Leviticus 16:18 and as the altar of burnt offering was first expiated and then used, Exodus 29:36 so it seems the altar of incense had not only an atonement made on it, but for it: and this was done

with the blood of the sin offering of atonement; by sprinkling the blood of that offering upon the horns of it, as we learn from the afore mentioned place; and this shows that Christ's mediation and intercession is founded upon the virtue of his blood, and the efficacy of his atoning sacrifice, see 1 John 2:1.

once in the year shall he make atonement upon it, throughout your generations; which proves the insufficiency of all legal sacrifices of themselves to take away sin, since every year, as the apostle observes, there was a remembrance of it, Hebrews 10:3.

it is most holy unto the Lord; either the atonement made on the day of atonement, which was a most holy part of service, and pointed at the great atonement made by the most Holy One, the Son of God; or this altar thus expiated, and devoted to sacred use, was reckoned a most sacred one to the Lord, and so was to have nothing offered upon it but what he ordered; with which Jarchi agrees in his note,"the altar is sanctified to these things only, and not to any other service.''