On Achdus

Rav Tzvi Yehuda Kook, the son of Rav Avraham Kook taught specifically how we must love heretics. He brings the example of Avraham who when told that Lot(very evil man) had been kidnapped during the war of the 4 kings against 5, he immediately went to war bringing his students and followers with him just to save an evil idol worshiper. Another example he brings is Moshe Rabbenu who came down the mountain to his followers worshiping the golden calf. G-d told Moshe he wanted to destroy the people, but Moshe said if you destroy them, I want you to destroy me too. He was also willing to give his life for the sake of idol worshipers. 

Rav Kook also taught that derech eretz precedes Torah. Our sages ask: why were the armies of Ahav(one of the most evil kings of Israel) victorious while King Saul fell in battle? Although Ahav was wicked, there was loyalty and love between the people of his kingdom at the time and Loshon Hara wasn't heard. In Bereahit Rabbah it is stated: so great is peace, even if people worship idols, yet there is peace between them, it were as if I(G-d) cannot pass judgement against them. In Saul's time, they were the greatest scholars and tzaddikim but there was little loyalty and love, and Loshon Hara was spoke.