1)
Why does it say that Yo'ash did not remember the Chesed...?
1.
Malbim: He repaid evil for good.
2)
Why did he say "Yere Hashem v'Yidrosh"?
1.
'Rashi' (20): They killed me because I was doing Hashem's Shelichus (saying my Nevu'ah). It is proper that Hashem seek (avenge) my blood. And so it occurred - the next year... (verse 23)
2.
Malbim: He asked Hashem to judge [and punish the guilty party].
