As part of his Tefillah to Hashem about Eisav, Yaakov says "הצילני נא מיד אחי מיד עשו", which means, "Save me from the hand of my brother, from the hand of Eisav" (בראשית ל"ב:י"א). Why does the Posuk have to say both "from my brother," and "from Eisav?" Everybody already knows that Yaakov has a brother and that his name is Eisav. Rashi (שם) implies that when a brother turns into an enemy, he becomes a much more dangerous enemy than a stranger. Others add, however, that just as a one-time beloved friend can become the worst enemy, so too when two enemies become friends it can become the strongest of friendships.
When one has difficulties getting along with someone, one should not think that just because at present he and the other party don't like each other, the bad feelings must last. On the contrary, if one will be able to overcome the animosity which he feels, these formerly negative feelings can be transformed into very positive feelings. On the international scene, we have seen countries who fought bitter wars against each other finally make peace and become allies. This should serve as a lesson for us in terms of making peace with individuals with whom we have fought in the past.