“And he did that which was right in the sight of the LORD, but not with a perfect heart.” -2 Chronicles 25:2
Amaziah’s heart was not right. He had godly actions, he did what was right in God’s sight, but his heart (attitude) was not devoted to God.
Service to the Lord our God comes from a heart of love to the Lord our God. The more you love Him, the more you desire to serve Him. If you serve God out of obligation, you will end up burnt out in serving Him.