His heart was lifted up - This expression generally occurs in a bad sense Deuteronomy 8:14; 2 Chronicles 26:16; Psalms 131:1; Proverbs 18:12; but here it must be taken differently. The margin “was encouraged” expresses fairly the true meaning. He first began by setting an example of faithfulness to Yahweh. He then proceeded to use his best endeavors to extirpate idolatry.
He took away the high places - Compare 2 Chronicles 20:33, and see the 2 Chronicles 15:17 note.