Rashi on Numbers 18:8/רש"י על במדבר י״ח:ח׳

1ואני הנה נתתי לך AND I, BEHOLD, I HAVE ALSO GIVEN THEE [THE CHARGE OF MINE HEAVE OFFERING] with pleasure. This is suggested by the word “Behold”, for this is an expression used when something is done with pleasure, just as in, (Exodus 4:14) “Behold, he goeth forth to meet thee and when he will see thee he will rejoice in his heart!” A parable! This may be compared to a king who presented a field to his friend, but he did not write or seal a deed of gift nor did he record it in the court. When a man came and laid claim to the field, the king said to him, “It seems that anyone who wishes to do so may come and claim against you; behold, I will write and seal a deed of gift to you, and record it in the court! So here, too, because Korah came and made a claim against Aaron to the Priesthood, Scripture (God) came and gave him the twenty-four “gifts” of the priesthood as an everlasting covenant of salt (i.e. an enduring covenant). For this reason is this section recording the gifts of the priests placed here after that which narrates Korah’s rebellion (Sifrei Bamidbar 117:1).

2משמרת תרומתי [I HAVE GIVEN UNTO YOU] THE KEEPING OF MY HEAVE OFFERINGS — This means that you have to keep them in a state of purity (to guard them against uncleanness).

3למשחה means as a distinction (cf. Onkelos; Sifrei Bamidbar 117:2; Zevachim 91a).