How did the early church grow from as few as 25,000 people at the end of the first century (100 AD) to as many as 20 million people two hundred years later (310 AD)? Now that's a question worth thinking deeply about. While considering this question we must note that Christianity was an illegal religion during this period (at best they were tolerated, at worst they were persecuted), they didn't have church buildings, they didn't have all of the Scriptures as we know them (the canon was still being formed), they had no professional leadership, they didn't have youth groups, worship bands, seminaries or commentaries, and they made it hard to join the church.
In his book, The Forgotten Ways, Alan Hirsch proposes that what they did have was what he calls Apostolic Genius - the inbuilt life force and guiding mechanism of God's people - and the living components or elements that make it up (a kind of missional DNA). Hirsch sees six ingredients as follows: Jesus as Lord, disciple-making, missional-incarnational impulse, apostolic environment, organic systems, and communitas (groups with a mission beyond themselves).
Could it be that the key to the future of the contemporary church is to get back to our ancient roots. Maybe, we need an 'ancient future' approach. We need to look back in order to move forward. After all, God always includes in the beginning of something the seeds of its ongoing effectiveness.
For those serious about seeing the church become all that God intends it to be in our generation, Alan's book is essential reading. In addition, I would highly recommend The Forgotten Ways Handbook, which is a practical guide for implementing the concepts presented in the book. This is an excellent resource for church leaders or ministry teams seeking to become more missional.