Seven rams - “A bullock and two rams” was the offering which God had required at the original consecration of the sons of Aaron Exodus 29:1; Leviticus 8:2. Jeroboam, for reasons of his own, enlarged the sacrifice, and required it at the consecration of every priest.
Related Commentaries of 2 Chronicles 13:9
2 Chronicles 13:9
9 Have ye not cast out the priests of the LORD, the sons of Aaron, and the Levites, and have made you priests after the manner of the nations of other lands? so that whosoever cometh to consecratea himself with a young bullock and seven rams, the same may be a priest of them that are no gods.