Parshas Bechukosai begins by telling the Jewish people that if they will follow Hashem's laws and keep His commandments and do them, many rewards and blessings related to the land and its productivity will then follow. These blessings include the statement ונתתי שלום בארץ"," which means that Hashem will bring peace to the land (ויקרא כ"ו:ו'). Rashi comments on this Posuk by stating "שהשלום שקול כנגד הכל," meaning that peace is equal to all other blessings combined. To support this, Rashi quotes a phrase from the ברכות קריאת שמע which we say during davening every day: "עושה שלום ובורא את הכל," which means that Hashem makes peace and creates everything, showing that peace is equal to everything else. This phrase in our Tefillah is actually based on a Posuk in Yeshayahu (מה:ג), which describes Hashem as "עושה שלום ובורא רע," "He who makes peace and creates evil."
The Be'eiros Yitzchok asks by what authority the אנשי כנסת הגדולה, the Men of the Great Assembly, who composed the Tefillos which we recite, were able to change the wording in the Posuk from ובורא רע"," "He creates evil" to "ובורא את הכל," "He creates everything." The Gemara in Berachos (דף י"א:) explains that the אנשי כנסת הגדולה did not intend to change the meaning of the text in Yeshayahu (שם), but they have the authority to change a word or a phrase if the result is a לישנא מעליא, a nicer way of saying it. It would appear, however, that this is not just a nicer way of saying רע, it's actually a change in meaning, since "evil" is not the same as "everything". In addition, there is another problem with this Posuk. The Posuk in Eichah ()ג': ל"ח says "מפי עליון לא תצא הרעות והטוב", "from the mouth of the "highest" (Hashem) does not come the bad and the good." This implies that it is not Hashem who creates the bad. The two Pesukim, then, in Yeshayahu (שם) and in Eichah (שם), are thus contradictory.
The Be'eiros Yitzchok explains that it was not in fact the intent of Yeshayahu to say that Hashem is the creator of evil. Rather, the רע which He creates has the potential to be good as well. Just as Hashem is the "עושה שלום", he is the בורא רע"" who converts what appears to be bad to us into something good. In life, what appears to be a tragedy often becomes something very positive and good. Many of us know this from personal experiences, and we also see it from the situation of the wicked Bilaam who came to curse Bnai Yisrael, but Hashem turned his words into Berachos. In truth, then, Hashem creates everything with the potential for good; even evil can potentially become good. Therefore, the אנשי כנסת הגדולה were able to change the text for our Tefillah to read עושה שלום ובורא את הכל, because that switch does not change the true meaning. When there is true peace, then everything, even the evil in the world, can become good.