John Gill Commentary Numbers 18

And the Lord spoke to Aaron
As the things spoken were such as concerned Aaron, he might be only and immediately spoken to: you, and your sons, and your father's house with you; meaning both priests and Levites, the priests by him and his sons, and the Levites by his father's house: shall bear the iniquity of the sanctuary; the blame of any evil committed there, the punishment of it; the priests, Aaron and his sons, if they did not perform the duty of their office aright, he in the most holy place, and they in the holy place, and at the altar of burnt offering in the court; and the Levites, if they did not take care to watch in the tabernacle, and keep out strangers and polluted persons.

and you, and your sons with you, shall bear the iniquity of your
priesthood; be answerable for my sins, errors, and mistakes that should be committed by them in the discharge of their office, through their own remissness, or not taking care that the Levites did their duty.

This shows that the office of priesthood, though honourable, was burdensome, and not to be envied; and that the people needed not to be under such terrible apprehensions as they were, lest they should come too near the sanctuary, as to be in danger of death, since it lay upon the priests and Levites especially to take care thereof, and who, if negligent, would suffer.

And to thy brethren also of the tribe of Levi, the tribe of
thy father
For his father Amram was of that tribe, and so the Levites were his brethren, as he is directed to consider them; which might serve to conciliate their minds, and make them easy with respect to his enjoyment of the priesthood:

bring them with thee ;
into the court of the tabernacle, for further they might not go: that they may be joined unto thee :
as their name of Levites signifies, persons joined and united to others, as they were to the priests: see reason of their patriarch's name Levi in (Genesis 29:34) ; and minister unto thee :
be assisting to the priests in killing the sacrifices, receiving the blood, and flaying the beasts, and in other things about the sanctuary, (Numbers 3:6) ;

but thou, and thy sons with thee, [shall minister] before the
tabernacle of witness ;
which was the most holy place, where were the ark of the testimony or witness, and the tables of the covenant; and they might be said to minister before that, when they ministered in the holy place, which was before it, when they burned incense upon the altar of incense, ordered the shewbread, and trimmed the lamps of the candlestick, which none but the priests the sons of Aaron might do.

And they shall keep thy charge, and the charge of all the tabernacle That is, the Levites, whatever Aaron and his sons, the priests, should charge them to do, or commit to their care and charge, that they shall observe; as to watch and keep out all unfit persons, to take down and set up the tabernacle when needful.

only they shall not come nigh the vessels of the sanctuary; as the ark and mercy seat in the holy of holies, the shewbread table, and candlestick in the holy place; wherefore when these were removed from place to place in journeying, they were covered, that they might not touch them as they carried them.

and the altar; both of incense and burnt offering, on neither of which might they offer.

that neither they nor you also die: the priests for suffering them to meddle with things that did not belong to them, and the Levites for intruding themselves.

And they shall be joined to you
As assistants in the sacred service: and keep the charge of tabernacle of the congregation, for all the
service of the tabernacle; (See Gill on Numbers 3:7) and (See Gill on Numbers 3:8); and a stranger shall not come near to you ;
not any of the other tribes, only such as were of the tribe of Levi; they only were to be brought with them, and joined to them, and assist them, and minister to them, as in (Numbers 18:2) ; though the Jews ^F8 understand by a stranger anyone that was not a priest.

FOOTNOTES:

• F8: Maimon. in Misn. Zebachim, c. 2. sect. 1.

And you shall keep the charge of the sanctuary
That is, the priests, Aaron and his sons; the high priest was to keep the charge of the most holy place particularly, and do what was to be done in that on the day of atonement; and the common priests to keep the charge of the holy place, and do everything relating to the altar of incense, the shewbread table, and candlestick:

and the charge of the altar ;
of burnt offering, which stood in the court of the tabernacle:

that there be no wrath any more upon the children of Israel :
as had been upon Korah and his company, (Numbers 16:32Numbers 16:33) , and as afterwards came on Uzziah, (2 Chronicles 26:19–21) .