The family is a unit of the church. Before a church can be there has to a family. The family cell then makes the church because the church is a subsection of the family
42 They devoted themselves to the apostles’ teaching and to fellowship, to the breaking of bread and to prayer.
The purpose of house groups is to spur growth and fellowship among the believers, giving them an opportunity to closely relate and share with one another as it is in scripture. Acts.2:42-46