John Gill Commentary 2 Chronicles 12:14

"And he did that which was evil, because he set not his heart to seek Jehovah." — 2 Chronicles 12:14 (ASV)

And he did evil
Committed idolatry, relapsed into that, his humiliation not being hearty and sincere:

because he prepared not his heart to seek the Lord ;
by prayer and supplication, and by an attendance on the service and worship of God; for though he did these things outwardly, yet not sincerely and heartily; he did not engage in them seriously and in good earnest, with affection and fervour.