והיתה לו ולזרעו אחריו ברית כהונת עולם
Preceding Pinchas’ act of zealotry, the only anointed Kohanim were Aharon and his sons, with every male child born afterwards immediately entering into the family as a Kohen. Pinchas, however, was already alive at the time that Aharon and his sons (of whom one was Elazar, Pinchas’ father) were designated as Kohanim. Only after Pinchas acted decisively to preserve the honor of the nation, and to glorify Hashem’s Name, Hashem designated him as a Kohen. In an alternative explanation, Hashem promised that all Kohanim Gedolim would descend from Pinchas. The Sefarim HaKedoshim explain that it was for good reason that…