English: “The sons of Aharon the kohanim” — the kohanim in their [proper] kehunah: this teaches that an ordinary kohen who served in the garments of a Kohen Gadol — his service is invalid.
In the sugya: Parallel to the reverse case on 1:7: rank-correct garments are required in both directions. An ordinary kohen in high-priest garments is not “the kohanim in their kehunah.”
Type of Learning
Diyuk from “the kohanim” — garments must match rank (ordinary kohen may not wear Kohen Gadol’s garments).
What Is Learned
An ordinary kohen may not serve in the high priest’s garments; mismatched rank of garments invalidates the avodah. “The kohanim” means the kohanim in their proper kehunah.