גדול פני תהדר ולא דל פני תשא ולא במשפט עול תעשו לא” (טו יט) “עמיתך תשפט בצדק
Chazal say (Shavuos 30a) that the passuk “betzeddek tishpot amisecha” does not only apply to the judgement of dayanim or baalei din, but also to the way each person needs to judge the action of another. Therefore, one who sees a friend doing something which is ambiguous – it is not clear if it is a sin or not - has a mitzvah to judge the friend favorably. Chazal say regarding the person who judges favorably (Shabbos 127b): “One who judges his friend favorably – is judged favorably.”
The commentaries differ on what Chazal mean “danim oso l’zechus.” Rav Eliezer of Metz, one of the Baalei Hatosafos, says that the word “oso” is about the one who is being judged favorably, meaning that because a person judges his friend favorably, then he causes that in the Beis Din Shel Ma’alah he will also be judged favorably, because there is a rule On High that when there is an action that can be judged for good or for bad, the middas hadin does not allow the person to be judged for good, until it is done in the lower world.
But the Shelah Hakadosh explains the word “oso” to apply to the “dan,” meaning, when someone judges his friend favorably, that someone is judged favorably On High, because “the action that a person does below, arouses a corresponding action On High.” The Shelah adds that one who is dan l’kaf zechus is also judged favorably for sins that he did “and the mekatregim have no power to prosecute against him.”
The Shelah further writes that because each aveirah that is done reduces the gilui Kavod Hashem in the world, then when a person judges his friend favorably, and determines that he did not sin, then Kavod Shamayim increases. Therefore, one who judges his friend l’kaf zchus has a double reward: “Not only is he judged favorably On High, Hashem shows him much love in this world as well.”
Shitah Mekubetzes Nedarim 40 1; Shnei Luchos Habris Sha’ar Ha’osiyos Kaf Zechus Os Beis
