Torath Kohanim (Sifra) on “tzav” (the classic source regularly cited by TT for this opening).
אין צו אלא לשון זירוז מיד ולדורות. אמר רבי שמעון: ביותר צריך הכתוב לזרז במקום שיש בו חסרון כיס.
Ein “tzav” ela leshon zeruz miyad uledoros. Amar Rabbi Shimon: beyoser tzarich hakasuv lezarez bemakom sheyesh bo chesaron kis.
“Tzav” is nothing other than a language of urging, for the present and for generations. Rabbi Shimon said: Scripture needs to urge especially in a place where there is monetary loss.
Custom — lexical force of “tzav” + the principle of extra urging where there is chesaron kis.
The command to the Kohanim concerning the olah is phrased with special urgency because the offering involves no personal monetary benefit for them.