Sefer Akeidas Yitzchok (Shaar 74) quotes the Sifri, who cites numerous sources in Chazal about the greatness of shalom.
Rav Elazar says: Shalom is so great that the prophets did not plant anything in the mouths of all creation besides for peace. Rav Shimon ben Chalafta says that shalom is so great that all brachos only end with peace, as is ‘Yevarechecha Hashem… Yair Hashem… Veyasem lecha shalom.’ Shalom is so great that it is needed even in times of war, as is stated (Devarim 20:10): ‘When you come close to a city to fight a war and you shall call to it with peace.’ Peace is so great that even the dead need it, as is stated (Bereishis 15:15): ‘And you shall come to your fathers in peace’, and it is stated (Yirmiyahu 34:5): ‘You shall die with peace.’
Shalom is so great that it is given to those who do teshuva, as is stated (Yeshaya 57:19): ‘Shalom, shalom to those far and near.’ Shalom is so great that it is given in the portion of tzadikim, as is stated (ibid:20): ‘Those who go with peace are put to rest in their resting place.’ Peace is so great that it is not put in the portion of the wicked, as is stated (ibid:21): ‘Hashem says that there is no peace for the wicked.’ Peace is so great that it is given to those who love Torah, as is stated (Tehillim 119:165): ‘Much peace to those who love Your Torah.’ Peace is so great that it is given to humble, as is stated (ibid 37:11): ‘And the humble shall inherit the world and they will enjoy it with much peace.’ Peace is so great that it is given to those who do tzedakah, as is stated (Yeshaya 32:17): ‘And the action of tzedakah is peace.’ Shalom is so great that it is Hashem’s name, as is stated (Shoftim 6:24): ‘And he called Him, Hashem Shalom.’ Rav Chananiah Segan Kohanim said: Peace is equal to the entire creation, as is stated (Yeshaya 45:7): ‘He created light and made darkness. He made shalom.’
He continues by saying that we see and amazing thing: The Sifri brings that Rav Eliezer ben Rav Elazar Hakafar says that peace is so great that even if the Jewish people is worshipping idols, the satan cannot harm them if they are at peace with each other. (This is learned from Hoshea 4:17.) But if there is machlokes amongst Klal Yisroel, they will be punished. He is saying that shalom is the key. When Hashem sees that we are at peace with each other, even if we are doing terrible sins like worshipping idols, He will not punish us right away and He will give us time to do teshuva. Even though worshipping idols is a very bad aveirah, the zechusim of shalom are so great that Hashem will push off the punishment for long enough for us to repent and return to Him. He will block the satan from harming us as long as we are united and at peace.