Why did he say "Havineni"?
Malbim: Aside from asking Hashem to show to him wonders and remove from him Derech Sheker, he asks also to understand simple Divrei Torah with understanding of the heart, a matter amidst a matter. This is Binah.
What is the difference between "Etzrah" and "Eshmerenah"?
Malbim: Notzer is more than Shomer. Something that one does not understand, even though he guards it not to transgress it, amidst fear of the Commander and his directive, he does not guard it like something dear and treasured.
What is "guarding with all the heart"?
Radak: It is not to acquire a reputation. Rather, it is with all my desire, amidst my love of Your Mitzvos.
Malbim: One who does not understand Divrei Torah, he guards them only amidst hope for reward and fear of punishment. When he understands its reasons, he guards it due to itself, with all his heart.
