The easiest way to imagine the spiritual underground is to first visualize the spiritual overground - the highly visible, well-intentioned and well-established network of churches, ministries and institutions that are the face of Christianity to our world.
In contrast, the spiritual underground is that less visible space, on the outskirts of Christendom, where unknown, unconventional and unlikely candidates do life and mission together in less-formal structures.
Historically, these misfits have been pioneers, who have contended for authenticity, honesty and original thought. In their passion to make a difference in the world, they have embraced praise and protest as being inextricably intertwined. For them, worship is not escapist: it has a social conscience. Although their efforts can appear to be a little scrappy, history has shown them to be surprisingly impactful. Their forward-thinking has triggered new ideas and given birth to new initiatives. Innovation in the underground has often resulted in the reformation of the overground.
Many bible stories show God instigating new stuff on the fringes of the established religious order. For example, the entrance of Jesus began with John the Baptist!