May you, kindly, explain to me why we should NOT seek vengeance and keep grudges, as specified for us not to do, in Leviticus 19:18?
You are asking a very good question. Why not “let him have it”?
Before getting to the reason for these mitzvot, it should be noted that it only applies to not taking revenge on another Jew, but not for taking revenge or bearing a grudge against gentiles. The whole verse reads, “לא תקם ולא תטור את בני עמך ואהבת לרעך כמוך אני ד'”‘”. Do not take revenge or bear a grudge against the people of your nation, love your friend as you love yourself, for I am G-d”.
The idea of נקמה-revenge is in order to rectify the wrong and injustice that was done. R. S. R. Hirsh (Genesis 4-15) explains the word נקם- to avenge, as being similar to the word יוקם, to “stand up” the justice that was violated
The Chofetz Chaim (Shmiras Halashon – Shar Hatevunah chapter 6 in the name of Smag, also see Rekanti regarding this mitzva) explains that one of the reasons for this commandment is because all of Klal Yisroel are considered one unit and one body. If someone’s hand hurts his head really hard, will he be angry at his foolish hand? Similarly, if another Jew hurts us, he is essentially like another part of ourselves. To take this a little further, if a person sees his two brothers fighting, he won’t take out a knife to one of them and chop off his hand. Why? Because he is his brother. Even though they are not physically attached, but they are from one father, one family, and come from the same soul and source.
Another example is of a rowboat of refugees that were rowing together to escape the Nazis. Each one had his ore and they tried rowing as fast as they could. One of the people on the boat noticed one of his friend’s food near him, and being very hungry ate it in front of him. The victim of the crime was very upset, but will he take his ore and throw it into the sea or hurt him in another way that he can’t row? Of course not. Why? Because they are one team with a common goal and hurting the other is essentially hurting myself.
It is the same with all Jews, we come from the same neshama, we are one family, and we also have the same goal- to get close to Hashem and have his presence dwell among us. Therefore, even if we are mad about what the other person did, it will hurt us if we hurt him.
In addition, the Ohr Hachaim (on that verse) explains that by taking revenge we actually cause a separation to Hashem’s name. All of Klal Yisroel have a part in His great name. By splintering Klal Yisroel, it causes a splintering to His name. This in turn causes the שכינה to depart from us, which brings great misfortune to all of us.
When we refrain from taking revenge on our fellow Jew, we show our love for G-d. In the verse of this commandment the Torah adds the words ”אני ד’”- I am G-d. The question is asked, “Why does the Torah add these words? One of the ראשונים says (Bechor Shor quoted in the sefer Lo TIkom pd. 252) that when one feels an urge to take revenge, his love for G-d should override his hatred for this person who wronged him. This should give him strength to withhold his anger. אני ד’, your love for Me should help eliminate your hate!
Aside from causing peace among us, a wonderful benefit of keeping these mitzvos, is a special hidden blessing with tremendous rewards. Chazal say, “כל המעביר על מדותיו מעבירין לו על כל פשעיו”, a person who passes by his feelings and character traits, will have all of his sins passed by.” One who is not particular and forgives the wrong done to him, will merit that G-d will forgive him for all his sins.רבינו יונה Rabeinu Yona (Shaarei Teshuva 1-28, also see Reishis Chochma Anava -3, and Shela Hakadosh (Shar Haosios Anava) says that this is מדה כנגד מדה. Since he overlooks evil done towards him, so too ד’ will forgive what he did wrong! (The opposite is unfortunately also true, as person that is meticulous about his honor etc., and doesn’t forgive others, will cause that G-d should also be meticulous with him and avenge all his iniquities).
Think about this for a minute. Isn’t this the best thing possible that we can have? Imagine how big each sin is, and how much pain and suffering it can cause us in world to come, when each moment of pain over there is worse than all the pain of this world. We should realize how much benefit we gain by forgiving one another, that G-d will remove all of that suffering from us. It is just unbelievable! This is similar to telling someone that if he is hurt by another without reacting harshly, he will be rewarded $10,000. Would any of us refuse such an offer? This is what we should keep this in mind when someone hurts us. True, you were really afflicted and to forget about it is really hard… but it is well worth it!
An additional reason we are commanded not to bear a grudge and not to avenge is because by avenging what is done wrong to us, we are essentially saying that the other person is the cause of the bad that befell us, therefore we want to right the wrong that did to us. Having such thought is forgetting that there is a supreme authority to the world, and things don’t just happen on their own. If G-d wouldn’t have wanted that this negative incident to happen to us, it wouldn’t have happened. Therefore, avenging the “cause” is to forget the real cause, of why it happened. thing. See Sefer Hachinuch mitzva 241-242.