Charles Ellicott Commentary 2 Chronicles 13:9

"Have ye not driven out the priests of Jehovah, the sons of Aaron, and the Levites, and made you priests after the manner of the peoples of [other] lands? so that whosoever cometh to consecrate himself with a young bullock and seven rams, the same may be a priest of [them that are] no gods." — 2 Chronicles 13:9 (ASV)

Regarding The priests of the Lord ... and the Levites, the Hebrew text seems to include the Levites among the priests of the Lord.

The phrase Cast out means Banished (Jeremiah 8:3).

The phrase After the manner of the nations of other lands literally means like the peoples of the lands; that is, priests from all classes of the nation, and not members of the divinely chosen tribe of Levi (see 1 Kings 12:31; 1 Kings 13:33). The surrounding heathen peoples had no exclusive sacerdotal castes.

The phrase So that whosoever cometh ... literally means, everyone who comes, that they may fill his hand with a steer, a son of the herd, and seven rams, becomes a priest to non-gods. “To fill a man’s hand” was the legal phrase for giving him authority and instituting him as a priest (Exodus 29:9; Judges 17:5).

Everyone who came with the prescribed sacrifices (see Exodus 29) was admissible to this new priesthood. The phrase “a young bullock and seven rams” is not a full account of the sacrifices required by the Law of Moses for the consecration of a priest. Perhaps Abijah did not care to be exact, but it is quite possible that Jeroboam had modified the Mosaic rule.

The compound substantive “no-gods” (lô’ ’elôhîm) is like lô’ ’êl and lô’ ’elôah (Deuteronomy 32:17; Deuteronomy 32:21). The calves are spoken of as mere idols, although there is little doubt that Jeroboam set them up as representations of the God of Israel.