מלך מוחל וסולח (בתפילת יוהכ"פ)
At first glance this phrase is not intended as a matter of request, since the form follows the description of the King (Melech). A King is unable to forgive his honor, and even if he forgives, his honor cannot be overlooked.
Therefore, sinners, before the King when spoil His honor, should not be able to forgiven.
Therefore, we must understand that after referring to HaShem as King, we also relate to Him as His children. Thus, even a King may forgive his children.
And one can now attempt to understand the actions of Moshe being angry regarding the group surrounding Korach that Moshe requested that HaShem not turn to their offerings (BeMidbar 16,15). Why didn’t Moshe follow the attribute of the Chachamim to forgive to one’s enemies?
As explained in Gemara Zevachim (120a) Moshe had the status of a King. Thus, Moshe was not allowed to forgive the people that slighted the honor the King, i.e. Moshe.
Another place (Yerushalmi B.K. 5,7) offers another reason why Moshe did not forgive Korach and this group. In that Gemara it explains that one should not obstinate and refuse to forgive. Rather, one should subdue the natural impulse and forgive another that has wronged you. However, there exists the circumstance of Lashon Hara where a person does not forgive forever.
In the circumstance of Moshe as explained in Sanhedrin 111, the verse (Bemidbar 16,4) says וישמע משה ויפל על פניו (and Moshe heard and fell on his face). What did Moshe hear? He heard that Korach and his group had warned their wives about seclusion with Moshe (indicating a suspicion about Moshe with a married woman). Thus, Moshe fell on his face (and could not find any alternative justification of their actions) and understood that Korach and his group had spoken Lashon Hara, and thus, it was impossible to forgive them.
