ולבניך לחק עולם למשחהתים אל אהרן ואני הנה נתתי לך את משמרת תרומתי לכל קדשי בני ישראל לך נת 'וידבר ה
G-d said to Aaron: 'Look! I have given you My gifts (which you must) guard (from ritual impurity). I have given you all the children of Israel’s holy things as a sign of greatness and to your sons as an eternal portion’ (Bemidbar 18,8)
למשחה Literally means for anointment
Targum Onkelos and Rashi render it לרבו for greatness; eaten in a manner fit for a king.
Rashi also says explains the early words in the verse, ואני הנה נתתי indicates that these gifts are given to the Cohanim with great joy בשמחה. Targum Yonoson ben Uziel likewise says “bechedva.” Hence, the Cohanim in return must consume the sacrifices with “moshchah” (nobility) which has the same letters as “simchah.”
Tosfos (Chullin 132b): without this verse one could thing the Cohen should eat the portion of the sacrifices (and all the other gifts to the Cohanim) to fulfill the mitzvah, not to receive enjoyment from it. This verse teaches that they may eat in whatever manner affords them the greatest pleasure. Thus, two concepts can be learned from the word למשחה: a) the meat should be eaten roasted (as kings eat); and b) the Cohen may eat in the manner that is most enjoyed.
The purpose of the anointing is for the greatness that goes to the Cohanim not as the result (reward) of their service but as recognition of their elevation to now be able to eat at the table of the King.
Rabbi Shimshon Hirsch: The same responsibility and care which is made the Cohen’s duty to have with Terumah, they are also to have for all holy items given by Hashem as gifts to the Cohanim for a continuous משיחה “anointment; i.e. given to be a continuous reminder for the separating out and keeping apart from everything low and not holy. This is the ultimate meaning of “anointing”. And only in anticipation of this “consecration” are they given to the priests as חק עולם, as an everlasting due.
למשחה בהם (Shmos 29,29) From this verse the Gemara (Yoma 5a) derives “appointment to office by particular clothing”; that is to say that there is a manner of making a Cohen into a Cohen Gadol by dressing in the garments of the Cohen Gadol. It would seem that this Gemara is the source of Rashi that this word indicates ruling.
However, Saadia Goan and the Ramban follow the simple meaning of anointment, and under the verse to mean that the Cohen Gadol will be anointed while wearing the special garments. “As the number of words is limited and the number of ideas that require representation in words if far greater (perhaps infinite), borrowing words for similar meanings is inevitable.” The Ramban also accepts this elsewhere (see Shmos 25,12). Similarly, the Tanya presents the concept of Tzadik in Chapter one as a borrowed term. The primary meaning of the word Tzadik is one who has no sins; but the borrowed, common meaning is one who is judged to more merits than sins.
Torah Temimah: One must understand the Gemara indicates that holy items may be eaten by the Cohanim in any manner that is most enjoyed. But they cannot eat the animals alive or only partially cooked.
Torah Temimah also explains that this derivation requires everyone to treat these special Cohanic gifts with proper respect and honor. Therefore, at a Pidyan haBen (redemption of the first born) ceremony the father of the child should stand the Cohen should sit as a sign of respect and honor.
