(1) And it came to pass on the eighth day.—That is, the day following the seven days of consecration. (See Leviticus 8:33) According to ancient tradition this was the first of the month Nisan, or March.

Moses called Aaron and his sons, and the elders.—That is, the same elders, the representatives of the people, who were called to attest the imposing ceremony of consecration (see Leviticus 8:3), are now also summoned to witness how the newly-installed priests entered upon the active duties of their ministrations. Like newly-born children who remain seven days in a state of uncleanness and enter into the covenant privileges of the congregation on the eighth day (see Leviticus 12:2-3), so the newly-created priests after a purging of seven days commenced their sacred duties and partook of their privileges on this symbolical day.

On the eighth day - i. e., on the first day after the week of consecration.

Le 9:1-24. The Priests' Entry into Office.

1-7. Moses called … Take thee a young calf for a sin offering—The directions in these sacred things were still given by Moses, the circumstances being extraordinary. But he was only the medium of communicating the divine will to the newly made priests. The first of their official acts was the sacrifice of another sin offering to atone for the defects of the inauguration services; and yet that sacrifice did not consist of a bullock—the sacrifice appointed for some particular transgression, but of a calf, perhaps not without a significant reference to Aaron's sin in the golden calf [Ex 32:22-24]. Then followed a burnt offering, expressive of their voluntary and entire self-devotement to the divine service. The newly consecrated priests having done this on their own account, they were called to offer a sin offering and burnt offering for the people, ending the ceremonial by a peace offering, which was a sacred feast. This injunction, "to make atonement for himself and for the people" (Septuagint, "for thy family"), at the commencement of his sacred functions, furnishes a striking evidence of the divine origin of the Jewish system of worship. In all false or corrupt forms of religion, the studied policy has been to inspire the people with an idea of the sanctity of the priesthood as in point of purity and favor with the Divinity far above the level of other men. But among the Hebrews the priests were required to offer for the expiation of their own sins as well as the humblest of the people. This imperfection of Aaron's priesthood, however, does not extend to the gospel dispensation: for our great High Priest, who has entered for us into "the true tabernacle," "knew no sin" (Heb 10:10, 11).Moses commands Aaron to offer a sin-offering, and burnt-offering, and peace and meat offering; the congregation drawing near, and so the glory of the Lord should appear to them; to make atonement for himself and the people, Leviticus 9:1-7. Aaron’s offering for himself, Leviticus 9:8-14; for the people, Leviticus 9:15-21, whom he blesses, first by prayer to God, and then by solemn declaration to them; the glory of God appears; fire from heaven consumes the sacrifice; the people shout and are amazed, Leviticus 9:22-24.

The eighth day, to wit, from the first day of his consecration, or when the seven days of his consecration were ended, Leviticus 8:33,35, as appears from Exodus 29:30, Ezekiel 43:27. The eighth day is famous in Scripture for the perfecting and purifying both of men and beasts. See Leviticus 12:2,3 14:8-10 15:13,14 22:27.

All the congregation were called to be witnesses of Aaron’s instalment into his office, to prevent their murmurings and contempt, which being done, the elders were now sufficient to be witnesses of Aaron’s first execution of his office.

that Moses, called Aaron and his sons, and the elders of Israel; Aaron and his sons to enter upon their office, by offering sacrifices for themselves, and for the people, and the elders to be witnesses thereof.

(a) After their consecration: for the seven days before, the priests were consecrated.