Leviticus 8:3

“And gather thou all the congregation together, etc.] That is, the heads of the tribes and the elders of the people, as Aben Ezra interprets it; for the whole body of the people, and every individual of them, could not be got together: unto the door of the tabernacle of the congregation; taking this for the whole court itself, as it sometimes is; though no doubt on this occasion as great a number was convened as well could be admitted into the court, or about it, to be spectators and witnesses of the solemn investiture of Aaron and his sons with the priestly office.”

“gather thou all the congregation together, &c.--It was manifestly expedient for the Israelitish people to be satisfied that Aaron's appointment to the high dignity of the priesthood was not a personal intrusion, nor a family arrangement between him and Moses; and nothing, therefore, could be a more prudent or necessary measure, for impressing a profound conviction of the divine origin and authority of the priestly institution, than to summon a general assembly of the people, and in their presence perform the solemn ceremonies of inauguration, which had been prescribed by divine authority.”

“Gather ... - Rather, gather all the assembly together toward the entrance of the tent of meeting. See Leviticus 4:13. The whole body of the people were summoned on this occasion, and the elders probably occupied the first places. The elders are especially called together in an unequivocal manner to receive directions to provide the first sacrifices for the nation to be offered by the newly consecrated priests Leviticus 9:1, and the body of the people afterward assemble as they do here Leviticus 9:5. The spot designated was the portion of the court in front of the tabernacle (see Leviticus 1:3 note). Toward this space the people were commanded to assemble to witness the great national…”

“All the congregation - The elders who represented all, and as many of the people as would, and could get thither, that all might be witnesses both of Aaron's commission from God, and of his work and business. Leviticus 8:12”

“Num 20:8, Num 21:16; Ch1 13:5, Ch1 15:3; Ch2 5:2, Ch2 5:6, Ch2 30:2, Ch2 30:13, Ch2 30:25; Neh 8:1; Psa 22:25; Act 2:1 Leviticus 8:4”