Catechism of the Catholic Church

Christ chose to be born and grow up in the bosom of the holy family of Joseph and Mary. The Church is nothing other than "the family of God." From the beginning, the core of the Church was often constituted by those who had become believers "together with all [their] household." When they were converted, they desired that "their whole household" should also be saved. These families who became believers were islands of Christian life in an unbelieving world. (759)