Sforno on Numbers 18/ספורנו על במדבר י״ח

1ואתה ובניך ובית אביך אתך תשאו את עון הקודש, you are responsible to prevent unauthorised people, i.e. ritually impure ones and non-priests from entering sanctified domains near the Tabernacle. This is a collective responsibility of all the priests. If unauthorized people nonetheless enter such domains due to inadequate surveillance you will be responsible for such a sin having occurred.

1וישרתוך, seeing their service is meant exclusively to assist the priests in their tasks.

2ואתה ובניך אתך לפני אהל מועד, whereas you and your sons will guard the Holy of Holies which forms the tent housing the Holy Ark containing the Tablets.

1ושמרו משמרתך ומשמרת האהל, the Levites are to guard the Holy of Holies (structure) which in itself is your domain; they are also to guard all the other sacred locations outside the Holy of Holies.

2אך אל כלי הקודש, the ones housed within the Tabernacle, comprising the Table, the Lampstand and the golden altar,

3they must not approach, whereas the copper altar although it is outside the walls of the Tabernacle they must not approach either.

1ושמרו את משמרת אהל מועד, within the curtained off area of the courtyard.

1'לכם מתנה נתוני לה, they are bidden on your behalf to carry out all these duties in connection with the Tabernacle.

1תשמרו את כהונתכם. To ensure that a non-priest, such as King Uzziah, does not enter the domain reserved exclusively for the priests.

2ועבדתם, priestly functions are to be carried out only by you the priests;

3the very fact that this assignment is in the nature of a gift for you, עבודת מתנה, makes it likely that outsiders are jealous and want a share of this. This is why you have to be especially on guard (to prevent interlopers from being punished by death.)

1ואני הנה נתתי לך, as for Me, in compensation for the careful security measures which you will take to preserve the sacred nature of these locations, I will grant you as exclusive gifts the potions listed forthwith.

1מן האש, for all of it was meant for burning on the altar, the priests having no share in it until after the parts which have to be burned up have been burned up. The reason is that the priests’ share is not really theirs, i.e. the sacrificial animal or parts of it does not belong to them, but it belongs to G’d and whatever they may eat, they eat as “guests at G’d’s table,” not in their own right, in Talmudic parlance משלחן גבוה הם אוכלים.

1This is also why בקדש הקדשים תאכלו, you are to eat it within the consecrated grounds of the courtyard of the Tabernacle.

1תרומת מתנם, what the owners of the animals in question give to the priests from the קדשים קלים, the offerings with a relatively lower level of sanctity, i.e. offerings in which the owners themselves have a share.

1כל תרומת הקדשים, such as that which is given to the priests of the thanksgiving breads, as well as the two loaves of newly harvested wheat presented on the Shavuot festival.כל תרומת הקדשים, such as that which is given to the priests of the thanksgiving breads, as well as the two loaves of newly harvested wheat presented on the Shavuot festival.

1ונחשב לכם תרומתכם, to ensure that blessing will be present in your homes even though we are speaking about something which has been measured, something not ordinarily subject to blessings. Our sages had gone as far as saying that when someone prays for G’d’s blessing on things he had already counted, measured, or weighed, this is a futile prayer, i.e. he uttered the Lord’s name in vain. (Taanit 5) This תרומת מעשר, tithe of the tithe is exempt from such restrictions.