1)
Why does it say that he did what is straight, but not with a full heart?
1.
Malbim (Melachim II, 14:3): He did Mitzvos by habit, unlike David, who served amidst love. Also Amatzyah's father Yo'ash served only because Yehoyada instructed him, and he veered from Hashem when Yehoyada died!
