Musar su Levitico 19:18

So is it [regarding] a man with his fellow: All Israel are relations of flesh, these with those. Since all of their souls are bound together, this one has a share in that and that one has a share in this. And hence it is not similar when the many do the commandments [to when they are only done by individuals]. And all of this is because of their being bound together. And our Rabbis, may their memory be blessed, thus explained (Berakhot 47b) about the one who is counted from the first ten in the synagogue - [that] even if a hundred come after him, he recieves the reward that corresponds to all of them. It is actually a hundred, as per its understanding. Since the ten are included - these in those - behold, they are ten times ten, one hundred. And [so] each one of them is composed of a hundred [parts]. If so, even if one hundred come [afterwards], he has the reward of a hundred. As so from this reason, Israel are guarantors for each other. Since each one actually has a part of his fellow - when the one sins, he damages himself and he damages the part that his fellow has in him. It comes out from the side of that part that his fellow is his guarantor. If so, they are the relation, one of the other. And hence it is fitting that a person be desiring of the good of his fellow and his eye be good towards the good of his fellow, and that his honor should be as beloved to him as his [own] - as he is literally him[self]. And from this reason were we commanded (Leviticus 19:18), "you shall love your neighbor as yourself." And it is fitting that he desire the propriety of his fellow and not speak about his disgrace at all. And he [should] not want it, in the way that the Holy One, blessed be He, does not want our disgrace nor our pain - from the reason of relation. So too [should] he not want the disgrace of his fellow nor his pain, nor his corruption. And it [should] be bad for him on account of [his fellow], as if he was actually experiencing that pain, or [good for him from] that good [that he experiences].

SINCE this quality is of a kind with the nature of the Creator, may He be greatly praised and mightily exalted, it is complementary to the twelve attributes especially characteristic of Him, i.e., the thirteen qualities which are ascribed to the Lord of Worlds, viz., "The Lord eternal is a merciful and gracious God," and so forth. That which it is possible for the wise man to aim at in action is, being slow to anger, "long-suffering," and largely generous, as it is said, "abundant in loving-kindnesses," tolerant of sin, as it is said, "Forgiving iniquity," and so forth. The upright and wise man must emulate these as far as he is able to do. Even as man desires that he be dealt with mercifully, when compelled to seek help, so must he be merciful to whosoever seeks his help. This quality is extremely praiseworthy, and God, exalted may He be, has distinguished His righteous servants through their love therefor. As thou knowest of Joseph, where it is said (Gen. xliii. 30), "His bowels did yearn upon his brother." The intelligent man has the qualities of pity and compassion implanted in his soul and ever present therein.

“You shall not take vengeance or bear a grudge against your countrymen.” (Leviticus 19:18). Our Rabbis, may their memory be blessed, said (Yoma 23a), “What is revenge [... If] one said to [his fellow,] ‘Lend me your ax’; he said [back] to him, ‘I will not lend to you, just as you did not lend yours to me’ - that is revenge. And what is bearing a grudge? [...] he said [back] to him, ‘Here it is, as I am not like you, who would not lend it to me.’” And the punishment for this is not for speaking, but rather for the grudge in the heart. And our Rabbis, may their memory be blessed, said (Yoma 23a) the [prohibition] on bearing a grudge is for monetary matters, but it is permissible to keep words of pride or disgrace or seeking evil [against him] upon his heart. And our Rabbis, may their memory be blessed, said (Yoma 22b), “Any Torah scholar who [when insulted] does not avenge himself and bear a grudge like a snake is not considered a Torah scholar.” But if they request forgiveness from him, he should forego his reckonings.