According to Daniel Peterson, kingship among the Nephites was a priesthood calling, and priestly ordination was primarily a royal prerogative. At least several of the Nephite kings--Nephi (2 Nephi 6:2)), Mosiah1 (Omni 1:12-22), Benjamin, and Mosiah 2--were also major prophets.
The notion of a priestly kingship is perhaps a bit jarring to modern readers, living in a society where church and state are kept separate as a matter of principle. But is should not be so disturbing to Latter-day Saints, whose aspirations for the life to come include becoming both “priests and kings” (D&C 76:56). After all, it seems that Christ, the true King of Israel, holds his kingship as a priesthood office.
The Nephites were not modern, and we should not be surprised to see them untouched by more recent institutions. Keeping this in mind, and being aware of this Nephite priest-king order of priesthood and government, it is striking that the small plates of Nephi do not record a single reference to any church actually existing in the New World, despite the fact that the small plates cover nearly the first five centuries of Nephite history. [Daniel C. Peterson, “Priesthood in Mosiah,” in The Book of Mormon: Mosiah, Salvation Only through Christ, pp. 189-190,200] [See the commentary on Mosiah 25:19,23]