John Gill Commentary 1 Kings 15:3

"And he walked in all the sins of his father, which he had done before him; and his heart was not perfect with Jehovah his God, as the heart of David his father." — 1 Kings 15:3 (ASV)

And he walked in all the sins of his father, which he had done before him Having such bad examples as both parents to copy after; it chiefly respects idolatrous practices, see (1 Kings 14:23).

and his heart was not perfect with the Lord his God He did profess the true God, and worshipped him, but not wholly, and only, and sincerely; he worshipped other gods besides him: and so his heart was not

as the heart of David his father Who was a sole and sincere worshipper of God, never departed from him and his service.