1)
Why does it say "Toras Hashem b'Libo"?
1.
Radak: Just like he instructs with his mouth, so is in his heart. His inside is like his outside.
2.
Malbim: He believes in Toras Hashem, and guards it in his heart.
2)
What is the meaning of "Lo Sim'ad Ashurav"?
1.
Rashi: His steps will not slip.
2.
Radak: Even one of his steps will not slip.
3.
Malbim: He will not slip from the ways of happiness. All his deeds and path is for happiness of the Nefesh.
