Heaven, earth, and I: the same root. Everything and I: one thing.
So when we practice together, we learn from one another. Individual practice is important, but when we only practice individually, it is difficult to see our limitations and our karma, the karma of our mind. The sangha is like a mirror, in which you can easily see your limitations, the limits of your actions and your opinions.
Together action is like a wave that carries you away and you cannot resist it. Your small self, your ego is too weak to resist that wave. This wave of together action is the wave of your true mind, of your true self. The name of it is – Just do it!