What is the significance of "va'Ya'amidem la'Ad l'Olam"?
Radak, Malbim: In the land, individuals perish but the species lasts [forever]. In Shamayim, the individuals themselves last.
Why does it say "Chak Nasan v'Lo Ya'avor"?
Rashi: Hashem set laws - this one serves during the day, and this one at night; they do not transgress that law.
Radak: The law that Hashem gave [to upper beings] at the beginning of their creation will never change. They will never change their order. Malbim - however, The laws that bound the land change, for in the land there is choice and desire.
Lev Eliyahu (Shemos p.135): If one stole wheat and planted it, it is proper that it not sprout (lest a sinner profit). However, the world goes according to its nature, and sinners will be punished in the future (Avodah Zarah 54b). Hashem does not change the nature that He established due to fools!
