After the burial of Yaakov, the Torah tells us that Yosef's brothers feared that he will take revenge upon them (Bereshis 50):

"And Yosef returned to Egypt, he and his brothers and all those who went up with him to bury his father, after his father's burial. And Yosef's brothers saw that their father had died, and they said: perhaps Yosef will hate us and will return to us all the evil which we have done to him. And they commanded (messengers) to Yosef to say: your father commanded before his death, saying: Thus say to Yosef: please forgive the sin of your brothers and their transgression, for they have done evil unto you. And now forgive the crime of the servants of you father's Lord. And Yosef wept when they spoke to him. And his brothers also went, and they prostrated themselves before him and said: behold, we are your slaves. And Yosef said to them: do not fear - am I in the stead of the Lord? And you intended evil against me (but) the Lord intended it for the good, in order to do, as (is happening) on this day, to sustain a great population."

The Ba'al HaTurim explains according to the Midrash, that the brothers' fear arose from the fact that on the way back from the burial of Yaakov, Yosef stopped next to the pit into which the brothers threw him, and said the blessing: "Blessed (is He) who performed a miracle for me in this place." They said to themselves that Yosef still remembers vividly that they sold him, and now he will take revenge upon them.

But there is one difficult word in these verses: Lu (Perhaps) Yosef will hate us. Indeed, most of the commentators, the foremost being Rashi, wrote that here the meaning of the word Lu is "perhaps" Yosef will hate us. As Rashi says:ֲLu (Yosef) will hate us – perhaps he will hate us. Lu has many meanings, and one of them is a term of request and an expression of a wish…

And lu also means "perhaps" - perhaps he will hate us, and there is no similar use of this word in the Tanach, and it expresses: maybe.

Nevertheless, there is a difficulty with this interpretation, since as Rashi writes, there is no other place where the word lu means perhaps. Generally the word lu means hallevai, which expresses a wish. And this requires clarification, as Yosef's brothers didn't want him to hate them. Exactly the opposite: they feared this possibility! So apparently the word pen (lest) would be more appropriate: lest Yosef will hate us.

The Tiferet Shlomo offers a new explanation which contains a great moral lesson: One of the worst feelings a person can have is when someone he wronged returns his bad deed with good. One is overwhelmed with shame because my friend, the one I have wronged, is standing up to a test in which I have failed. The Tiferet Shlomo writes that the meaning of the word lu is indeed hallevai – "may it be" – and Yosef's brothers really wished, in the secret depths of their hearts, that Yosef would hate them. They inflicted evil upon Yosef, and in return Yosef did them only good. This caused them shame and uneasiness.ֲֲֲ 

If one offends his friend grievously, and in spite of that he feeds him and does him all the good things possible - the shame is devastating.ֲֲֲ 

As it is written regarding Yosef's brothers: "May Yosef hate us." Since they could not bear the shame they felt before him, since they maltreated him and he did them only good, and sustained them, their wives and their children. It is known that there is no measure to this anguish.

Similarly he explains the verse (Daniel 9:7) "Yours, HaShem, is the tzedakah (charity, righteousness) and our (lot) is to be shamefaced." That is, the more good HaShem does us - more and more tzedakot which we don't rightfully deserve - the more our shame increases before Him, since we very often sin toward Him, and HaShem gives us good in return for our evil.

And the converse is also true: when a person is wronged and he overcomes the impulse for revenge and does good to the offender, this is the best reaction possible. On one hand he does good toward him and does not transgress the prohibition of taking revenge, and on the other hand he causes him to feel the shame we mentioned – that he mistreated him, and that the offended one, in contrast to the offender, returned him good in return for evil. And it is possible that this can awaken him to thoughts of repentance, and the desire to make amends.

And Shlomo says in Mishlei (25):

"If your enemy is hungry feed him bread, and if he is thirsty give him water. For you are stoking (hot) coals on his head and HaShem will reward you."

And the questions arise: why give bread and water to your enemy? And why is this equated to stoking coals on his head, when in practice you are doing him good?

In light of what we have explained, the reason is clear: Exactly by giving him bread and water, and therefore showing him that you - in contrast to him – are doing good, this makes him feel much worse that if you would retaliate with evil. This induces an inner burning pain which can awaken thoughts of repentance, as there is no limit to this kind of suffering which results from these pangs of shame which come when one sees that his fellow man does not succumb to the evil inclination and manages to reciprocate with good in return for the evil which was done to him.

And the Malbim writes on this verse: "If your enemy is hungry feed him bread": The advice to one who wants to exact a great vengeance on his enemy is not by denying him bread and water, but to the contrary – by doing him only good: if he is hungry feed him, and if he is thirsty give him water to drink, and this way you will gain two things:

1. "For you are stoking coals on his head": doing him good is likened to stoking coals on his head, because he will remember that he wronged you and injured you, and will be shamed and humiliated because now he must receive bread and water from you in return for his evil.

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1. "And HaShem will reward you": You will receive reward from HaShem for the tzedakah which you give him, and if you take revenge by not giving him, you will not be rewarded.

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Therefore, the Malbim adds: this kind of "revenge" is permitted, since it originates from good - You benefit your enemy instead of reciprocating with evil for evil, and HaShem will give you a good reward for your deed.