Sforno on Exodus 22:28/ספורנו על שמות כ״ב:כ״ח

1מלאתך, the heave for the priest of your grain harvest. The word מלאה appears to be borrowed from Genesis 41,22 where the good ears of corn in Pharaoh’s dream are described as such.

2ודמעך, the parallel heave from your oil and grape harvest.

3בכור בניך תתן לי, to perform all kinds of sacred duties. This includes service in the Temple, teaching Torah, something which in later periods became the foremost occupation of the priests, commented upon by Maleachi 2,7 with the line כי שפתי כהן ישמרו דעת והתורה יבקשו מפיהו, “for the lips of a priest guard knowledge, and men seeking rulings from his mouth, for he is a messenger of the Lord of Hosts.”