I love this quote, it strikes right at the heart of safe, comfortable, fellowship-only Christianity. It is a quote from Martin Luther which is quoted by Dietrich Bonhoeffer in his brilliant book "Life Together".
"The Kingdom is to be in the midst of your enemies. And he who will not suffer this does not want to be of the Kingdom of Christ; he wants to be among friends, to sit among roses and lilies, not with the bad people but the devout people. O you blasphemers and betrayers of Christ! If Christ had done what you are doing who would ever have been spared?" (Martin Luther)