"The family cannot be limited to the modern atomistic family, those living under one roof as husband, wife, and children. The marriage unit of husband and wife is the nuclear family, but it is not the sum total of the family. To illustrate: on the one hand, a family with three children, nominally religious, is in no sense Christian nor an area of dominion. Each member goes his own way: there is no sense of any moral responsibility to God or to one another, nor to the grandparents. This is a marriage and a family, but in a biological sense and a legal sense, not in a Christian or moral sense, in that even adultery and fornication are tolerated within limits. In another case, the family has three children, two sons, and one daughter. A son and daughter have never married; all three children reside some distance from home. They are, however, a godly family. The parents are supported in retirement by the unmarried son and daughter, with help from the other son. The married son was helped through the university by his brother and sister. The family has helped other relatives, and some friends as well, and, while absent from their small town home, have been important in aiding some Christian causes therein. All three children are exercising dominion under God, and all three have a strong sense of family. The daughter, nearing retirement herself, has more of a family life in her effect on other families, and the love she has earned, than the lawless mother in the first family. In the first family, family life means little more than a legal sexual relationship and life under one roof, an essentially biological concept of family life. In the second family, family life is a form of social organization with theological premises, so that it exists and governs where no sexual relationship exists...

"The family in Biblical law controls three central areas of life, the control of which governs society. And institution or agency which controls children, property, and inheritance is the determining agency in any society. Not surprisingly, the modern state, in its totalitarian designs, has invaded all three areas in varying degrees, by means of property taxes, inheritance taxes, statist schools, and laws limiting the jurisdiction of the family. The state seeks to be the new family of man."
~ R. J. Rushdoony, "Marriage and the Family," from Salvation and Godly Rule.