Adam Clarke on 1 Kings 12:31

A house of high places - A temple of temples; he had many high places in the land, and to imitate the temple at Jerusalem, he made one chief over all the rest, where he established a priesthood of his own ordination. Probably a place of separate appointment, where different idols were set up and worshipped; so it was a sort of pantheon.

Made priests of the lowest of the people - He took the people indifferently as they came, and made them priests, till he had enough, without troubling himself whether they were of the family of Aaron or the house of Levi, or not. Any priests would do well enough for such gods. But those whom he took seem to have been worthless, good-for-nothing fellows, who had neither piety nor good sense. Probably the sons of Levi had grace enough to refuse to sanction this new priesthood and idolatrous worship.