Unity is essential for perfecting the world and for sustaining everything. God is very pleased when there is unity, so much so that our Sages said that the Divine Presence only dwells among Yisrael when they are united. More, that when the Jewish people are united, the Attribute of Justice cannot dominate them.
Any group that wants to accomplish something enduring, must be bound in unity as one, and then all the tempests of the world will not move them from their place. But if one says this and the other says that, then they break into factions, which leads to disharmony and eventually it causes much calamity. This is like a bundle of reeds: as long as they are tied together, even the strongest man is not able to break them, but when they are separated, they are easy to break.