Why do we forgive past incarnations every night?

Question

In the first paragraph of Krias Shema Al Hamita, we say that we forgive:

...לְכָל־מִי שֶׁהִכְעִיס וְהִקְנִיט אוֹתִי אוֹ שֶׁחָטָא כְנֶגְדִּי בֵּין בְּגוּפִי בֵּין בְּמָמוֹנִי...

...anyone who has angered me, or sinned against me, either physically or financially...

My question is on the phrase:

...בֵּין בְּגִלְגּוּל זֶה בֵּין בְּגִלְגּוּל אַחֵר...

...in this incarnation or in any other...

How come every night we say that we forgive people from previous incarnations, it's not like someone can bother us in the past from last night until tonight?

Answer 1

R Yisroel Reisman in his book Pathways of the Prophets asks exactly your question (p. 440) and answers

In a previous life, Reuven may have lived as Yaakov. Today Yaakov is no longer alive. Still, Yaakov's enemies may be speaking lashon hara about him, even today. A person should want to forgive even these sins. Thus, each and every day he forgives anyone who sinned against Yaakov, his previous self.

Answer 2

Rabbi Eliezer said: “Repent one day before your death.” So his disciples asked him: “Does a person know which day he will die?” Rabbi Eliezer responded: “Certainly, then, a person should repent today, for perhaps tomorrow he will die—so that all his days he is repenting.” (Talmud, Shabbat 153a)

Part of repenting is to forgive those who have wronged us and then asking God to forgive us as well for our sins just like we have forgiven others.

So, perhaps in a previous Gilgul you were not religious and/or did have a chance to forgive this person and so you are forgiving him now.

But why every night, though? Perhaps during the day you came into contact with this Gilgul that affected your Gilgul and there was an altercation that was a continuation of the issue from long ago.

There are stories of Souls who quarreled previously coming back down and quarreling again, as related here:

A report, the purpose of which is to explain the disagreement between the Baal Shem Tov and Rabbi Nahman of Kosov, relates that the Baal Shem Tov was a spark of the soul of King David, while Rabbi Nahman was a spark of the soul of Saul.

-- Shivhei Ha-Besht, p. 92; Beit Avraham, by Rabbi Abraham of Slonim (Jerusalem, 1973), p. 161

Answer 3

The Derech Hashem (2:3:10) writes

מקרים לאדם מצד גלגול נשמתו: עוד שורש אחר נמצא להנהגה בעניני העה״ז והוא שהחכמה העליונה סידרה להרבות עוד ההצלה כמ״ש שנשמה אח׳‎ תבא לעה״ז פעמים שונות בגופים שונים ועי״ז הנה תוכל לתקן בפעם א׳‎ את אשר קלקלה בפעם אחרת או להשלים מה שלא השלימה ואולם בסוף כל הגלגולים לדין שלע״ל הנה הדין יהיה עליה כפי כל מה שעבר עליה מן הגלגולים שנתגלגלה ומן המצבים שהיתה בם Afflictions to a man from the reincarnation of his soul: There is [yet] another principle found in the direction of the matters of this world. And that is that the Supreme Wisdom arranged to expand salvation more, as we have mentioned, such that one soul comes to this world at various times in different bodies. And behold through this, it may repair at a different time what it corrupted in a [previous] time; or perfect what it did not perfect. However at the end of all the incarnations in the judgement in the future to come, the trial will surely be regarding [the soul], according to all of the incarnations that it experienced and all the states in which it existed.

We are here to repair ourselves and our world using all the resources, talent, etc. at our disposal. If we don't succeed at first, we might return to this world to try fixing ourselves and our world again under different circumstances. Then we might return yet again after another failed attempt. During Krias Shema Al Hamita, we are forgiving anyone who has harmed us in any way, whether in this lifetime or a previous one. Why? When another is punished on our account, we too suffer some of the consequences. Chazal say one cannot be mekabel pnei haShechina while others are punished on their account. We don't wish that on ourselves, and we don't wish that damage on the world - whether in our current lifetime or previous ones, because they are all intertwined.

Moreover, the Mishna Berura (239:9) adds that forgiving those who harmed you will grant you a long life - גם ראוי למחול לכל מי שחטא כנגדו וציערו ובזכות זה האדם מאריך ימים. Following the Gemara Megillah (28a) listing why each individual merited a long life:

וְלֹא עָלְתָה עַל מִטָּתִי קִלְלַת חֲבֵרִי כִּי הָא דְּמַר זוּטְרָא כִּי הֲוָה סָלֵיק לְפוּרְיֵיהּ אֲמַר שְׁרֵי לֵיהּ לְכׇל מַאן דְּצַעֲרָן Rabbi Neḥunya also said: Nor did I ever allow the resentment caused by my fellow’s curse to go up with me upon my bed. This is referring to conduct such as that of Mar Zutra. When he would go to bed at night, he would first say: I forgive anyone who has vexed me.

With that premise in mind, we aspire to forgive others from previous gilgulim each night because some of the tests we faced today may very well have been a rerun of a failed test in a previous lifetime. For instance, if Reuven sideswiped your wagon in the 1800s but didn't pay, and you didn't forgive him since the damage was never renumerated, then if he's granted the opportunity to fix what he broke once again, you and Reuven will come back in the 2000s and he might sideswipe your car. Maybe he'll fail the test once more and decide to hit-and-run. It's now up to you to forgive this person. You certainly don't have to, but you might come back again in the 2050s and he'll sideswipe your hover car all over again. Since we never know which of today's tests are "new episodes" or "reruns" from a previous lifetime, it's wise to forgive everyone who harmed us each day. Helpful for them to finally be let off, but most helpful for us not to need to return all over again.