1 Pt 2:9 is paraphasing Ex 19:6, which didn’t seem to prohibit a distinct, ordained priesthood in Judaism.
Not only did the usage in Exodus exclude any pejorative sense in the reference to the Melchizedek order of priesthood, but the Hebrews 5:6 reference to Jesus being of that order shows that calling of priesthood to be the loftiest state of the term.
HF