Musar for Yoma 45:15

And there is yet another reason for this. It is known that in accordance with a man's ordering of his traits in this world is the corresponding arousal of this trait in the world above. If it is his way to overlook offenses and to deal with men with the traits of lovingkindness and mercy, he thereby arouses, above, the trait of mercy, and the Holy One Blessed be He is merciful to the world because of him. And "from the fruits of a man's mouth, his soul will be sated." And he, too, will merit the mercies of the Holy One Blessed be He, and his offenses will be forgiven, as Chazal have said (Shabbath 151b): "All who are merciful to men are granted the mercies of Heaven," and (Yoma 23a): "All who overlook offenses to themselves have their [own] offenses overlooked [by Heaven.]" As stated in the Zohar, Parshath Emor:

We shall explain our words: Even if he were not forgiven through this [savlanuth] only for one sin completely, but would only have his punishment [somewhat] attenuated, it would suffice him [to suffer this denigration]. How much more so if he were forgiven completely for one sin. And how much even more so now that we know that he is forgiven for all his sins, even those which are called "pesha" [offense], (so long as he takes heed not to commit them from now on.) As Chazal have said (Rosh Hashanah 17a): "If one forgives slights against himself, all of his offenses are forgiven, as it is written (Michah 7:18): 'He forgives transgression and passes over offense.' Whose transgression does He forgive? The one who 'passes over' [i.e., overlooks] offense."