There's a limit to the number of people with whom we can effectively maintain a relationship and that number is a maximum of about 150. Interesting that the gathering of Jesus' followers after his ascension numbered about 120.
There's a brilliant exposition of this theory by David Wong, What is the monkeysphere? (some-rude-words alert) which roots it in everyday life, even if you don't entirely agree with all of David's conclusions.
Something happens when we get more than 150 people together – we lose touch. Think about the churches you know. What do the ones with up to about 120 people feel like compared with the ones that have 180 or more? Interesting!