The power of meditating together

A few weeks have past since the first meeting of interested people for the teachings of Eckhart Tolle. I spoke with a lot of people about this new project: "Ahh interesting! Yes I know Eckhart Tolle, he is a funny man. I've read his book the Power of Now"  was the common reaction. My invitation to join a Local Group Meeting is for most a completely new possibility that people have to get used to. How can I explain the power that is released when more people meditate together? The benefit from this for everyone's individual process as well as the awakening process of the world -without sounding like a saleswoman- ?