Albert Barnes Commentary 2 Chronicles 15:12

"And they entered into the covenant to seek Jehovah, the God of their fathers, with all their heart and with all their soul;" — 2 Chronicles 15:12 (ASV)

Solemn renewals of the original covenant that God made with their fathers in the wilderness (Exodus 24:3–8) occurred from time to time in the history of the Jews, following periods of apostasy. This renewal in the reign of Asa is the first on record. The next occurred 300 years later in the reign of Josiah, and a third took place in the time of Nehemiah. On such occasions, the people bound themselves by a solemn oath to observe all the directions of the Law, calling down God’s curse upon themselves if they abandoned it.