That mainline churches are shrinking in attendance shouldn't be surprising for the simple reason that they have been and are theologically disconnected from the existential base of all life - what is - nature, the root consciousness of life, of theology.
If we get nature wrong we get theology wrong. Even as they are leaving church, people are awakening to a new ecological sensitivity - what Pope Francis is about. Universally, true religion has values in common - there is no hopeful future if we, as church, fail to awaken to our commonality and join in-common in nature-sensitive effort.