Rashi on Numbers 3:10/רש"י על במדבר ג׳:י׳

1ואת אהרן ואת בניו תפקד AND THOU SHALT CHARGE AARON AND HIS SONS — The word תפקד is an expression for “appointing” and not an expression for “counting” (although it is Kal, and usually “appointing” is expressed by the Hiphil of the verb; cf. Rashi on Numbers 1:50).

2ושמרו את כהנתם AND THEY SHALL KEEP THEIR PRIESTS OFFICE — the receiving of the blood in holy vessels, the sprinkling of it, the burning of the fat and the other rites which are entrusted to the priests’ charge.