The Art of Forgiveness

 https://www.chabad.org/library/article_cdo/aid/1619314/jewish/The-Art-of-Forgiveness.htm

Why should one forgive?

Basically, because it is a mitzvah, a divine command. The Torah explicitly forbids us to take revenge or to bear grudges (Leviticus 19:18). It also commands us, “Do not hate your brother in your heart” (ibid. 19:17).