1)
Did he eradicate only the Asheros?
1.
Rashi: He eradicated also the Bamos, like it says above (16:6).
2)
Why did he mention these two merits?
1.
Malbim: Eradicating the Asheros corresponds to [protected you from punishment for] sinning in deed. Preparing your heart to seek Hashem corresponds to sinning in thought.
