What is the significance of His eye not having mercy?
Malbim: Chas is not destroying a matter, for he has a need for and benefit from it, e.g. "v'Einechem Al Tachos Al Kleichem" (Bereishis 45:20). Chomel does not destroy because the matter is good and beautiful, and it is improper to destroy it ? "Chamal ha'Am Al Meitav ha'Tzon" (Shmuel I, 15:15), in order to offer them to Hashem 1 . Hashem will not be Chomel, for the ways of your Nefesh are not beautiful ? they are corrupt! "Mashchasam Bahem Mum Bam Lo Yeratzu" (Vayikra 22:25). I will not be Chas due to benefit that I get from you 2 , for "your abominations are in you." All are evil ? no need or benefit can come from you.
They did not want to bring Korbanos for a need or benefit, just they deemed it improper to destroy nice animals (PF). They thought that offering them for Korbanos would fulfill "v'Hacharamtem" (ibid. 15:3; refer to Shmuel I, 15:20:3:1).
Hashem does not need or benefit from anything. However, He considers it a benefit when His will is done. (PF)
