The cell group is a form of church organization that is used in many Christian churches. Cell groups are generally intended to teach the Bible and personalize Christian fellowship. They are always used in cell churches, but also occur in parachurch organizations and other interdenominational settings, where they are usually referred to as such as Bible study groups. In Methodism, they are known as class meetings and are a means of grace; in Catholicism, they are known as basic ecclesial communities. The cell group differs from the house church in that the group is part of an overall church congregation, whereas the house church is a self-contained congregation. Terminology The term cell group is derived from biology: the cell is the basic unit of life in a body. In a metaphorical sense, just as a body is made up of many cells that give it life, the cell church is made of cell groups that give it life. These groups are known by a variety of other names, including life groups, small groups, home groups, classes or class meetings (used historically in Methodism) and fellowship groups. Colin Marshall uses the term growth group, suggesting that the aim is for group members to "grow in Christ", and, through the group, for the gospel to "grow and bear fruit." Another term, typically employed in Missional Communities, is huddle. This refers to a small group in which discipleship is emphasized and in which membership is by invitation only. History Christian Bible David Hunsicker points out that while house churches are mentioned in the New Testament, the institution of a "well-organized, structured church" resulted in the decline of the small home groups. Radical Reformation The concept was resurrected at the time of the Radical Reformation and "Ulrich Zwingli inadvertently pushed the Anabaptists in the direction of small groups when he started meeting with a small gathering of men who were interested in learning New Testament Greek. The concept of small groups was revived again in the late seventeenth century by Anthony Horneck in Great Britain and Philipp Jacob Spener in Germany. Pietistic Lutheranism Philipp Jakob Spener published his Pia Desideria in 1675 and laid out his program for the pietistic revival of the Lutheran Church, emphasising the use of small groups. He suggested the reintroduction of "the ancient and apostolic kind of church meetings," held "in the manner in which Paul describes them in