Dogen instructed,

It is said in the secular world that a castle falls when people start to whisper words within its walls. It is also said that when there are two opinions in a house, not even a pin can be bought; when there is no conflict of opinions, even gold can be purchased. Even in the secular world, it is said that unity of mind is necessary for the sake of maintaining a household or protecting a castle. If unity is lacking, the house or the castle will eventually fall. 

Much more, should monks who have left home to study under a single teacher be harmonious like the mixture of water and milk. There is also the six ways of harmony - that of body, mouth, and mind, keeping the same precepts, having the same insight, and carrying on the same practice. Do not set up individual rooms, nor practice the Way separately either physically or mentally. 

Our life in this monastery is like crossing the ocean on a single ship. We should have unity of mind, conduct ourselves in the same way, give advice to each other to reform each other’s faults, follow the good points of others, and practice the Way singlemindedly. This is the Way people have been practicing since the time of the Buddha (Shobogenzo Zuimonki, Book 4, Chapter 13).