What is "Pela'os"?
Rashi: They are covered 1 and wondrous beyond [the understanding of] man. There are light Mitzvos for which You gave great reward, such as Shilu'ach ha'Kan.
Malbim: In the Edos of the Torah, the simple meaning of the tales is true, but there are also secrets and hidden matters, e.g. Gan Eden, the rivers [that come from it], the snake, the Nefilim, and the kings who reigned in Edom...
Radak: This is like "Ki Yipalei Mimecha Davar" (Devarim 17:8). The essence of the Mitzvos and their reasons and wondrous, with many branches; intellect could not teach them.
How could David say "Pela'os Edvosecha"? Moshe said "Ki ha'Mitzvah ha'Zos Asher Anochi Metzavecha ha'Yom Lo Nifleis Hi Mimecha" (Devarim 30:11)!
Radak: "Lo Nifleis" means that it is not a metaphor, and you do not know how to understand it; "Karov Elecha ha'Davar Me'od b'Ficha uvi'Lvavecha La'asoso" (Devarim 30:14). Like you learn it with your mouth, so you understand it in your heart, and so you will do it. It is not a mere metaphor. This refutes Notzerim who said that it is.
What is the meaning of "Netzarasam Nafshi"?
Radak #1: He put his eyes on them greatly to understand them.
Radak #2: He guarded them to do them, for he understood them and knew their benefit. One who does not understand a Mitzvah will not guard it properly.
Malbim: Something hidden requires extra guarding.
