2 Chronicles 17:6 Commentary - English Annotations on the Holy Bible by Matthew Poole

His heart was lifted up above all discouragements, and difficulties, and fears, by which men’s hearts use to be cast down: he was valiant and resolute for God and his ways.

He took away the high places and groves, to wit, such only wherein idols were worshipped, as appears by comparing this with 2Ch 20:33. And though Asa had done this before, yet either he did not do it thoroughly, or the Jews (who were many of them mad upon their idols) had secretly made new ones, in the latter part of his reign, when he grew more infirm in body, and more remiss in God’s cause.