I've never really thought of "John Piper" and "small groups" in the same thought, but here is this very well-spoken pastor encouraging his church to get involved in a small group, and sharing why it is important.
Lately, I have been trying to update the definition of Sunday Schoo/Small Groups. The age-old axiom is this:
Sunday School is the church organized to do the work of the ministry.
My new definition is simply a 21st century expression of the one above:
Small Communities is how the church organizes for mission.
It is imperative for church leaders to understand that the church's classes and groups need to be the organization carrying the major responsibility to carry out the church's mission of making disciples. This is best done by impacting lostness in the culture, bringing them to repentance and salvation in Christ, and then walking with people in their journey as Christ-followers.
I am finding it very common now for churches to assign the church's mission to the missions team, or the youth group, or through broad appeals from the platform to just go. Our classes and groups want to be involved in the core mission of the church, and should be the platform through which the church organizes itself for mission. Smaller groups are easier when it comes to understanding mission, communicating mission, and also for accountability.