The author seeks to develop a practical theology of small groups using a Neo-Barthian approach. It's a good book, which seeks to help us understand that small groups do more than help the church grow (or keep the folks happy). It is the outgrowth of a Princeton Ph.D. in Practical Theology. It's an academic treatise, not a how-to manual.
The author uses Barth's concept of koinonia, which emerges from his view of the Trinity, to help us understand the nature of the divine/human interaction and human/human interaction. It invites us to remember that truly Christian small groups will not be homogenous -- a gathering of the birds of a feather -- but will seek to incarnate the diversity present in church and community.
It's a good book, but recognize that its an academic piece.