Albert Barnes Commentary 2 Chronicles 15:17

"But the high places were not taken away out of Israel: nevertheless the heart of Asa was perfect all his days." — 2 Chronicles 15:17 (ASV)

When comparing this verse with related passages, it seems that in 2 Chronicles 14:3 and 2 Chronicles 14:5, the writer has the king's intentions and efforts in mind, while here he is speaking of the people's practice. However earnestly the most pious kings sought to root out the worship at the high places, they failed to achieve complete success. A similar discrepancy, which can be explained in the same way, is found in the history of Jehoshaphat (compare 2 Chronicles 17:6 and 2 Chronicles 20:33).

The heart of Asa was perfect all his days. This does not mean that Asa was sinless (see 2 Chronicles 16:2–10; 2 Chronicles 16:12), but that he was free from the sin of idolatry and remained faithful to Yahweh all his life.