TT #161 · Parashas Shoftim · Third Aliyah · Passuk 18:05
For the Eternal your God has chosen him from all your tribes to stand and serve in the name of the Eternal, he and his sons, all the days.
Torah Temimah points to Sifrei Devarim 167.
TT lemma: לַעֲמֹד לְשָׁרֵת.
English: ‘To stand and serve in the name of the Eternal’ – this is the Temple service.
Derash identifying the service (Sifrei) — the standing and serving refer to the avodah of the Mikdash.
The kohen is chosen to stand and perform the service of Hashem; this is the rationale for his unique status and support.