In the absolute sense, the purpose of marriage is, as everywhere, God's glory. Then, besides the good that husband and wife are to have from each other in the estate of marriage (Ge 2:18; Eph 5:25-29,31; Col 3:19), its purpose is the raising of the next generation in the discipline and admonition of the Lord (Eph 6:4; Col 3:21; Dt 6:7,20, Pr 19:18). The chief obligation of parents toward children consists in this, and children in turn owe parents obedience (Ex 20:12; Eph 6:1; Col 3:20).
The Christian home is a miniature of the church within the church (ecclesiola in ecclesia), whose priest is the head of the home. Therefore divine service must not be lacking (Dt 6:7; Ge 18:19; 2 Co 12:14). Obviously the scope of the household's divine service cannot include that which belongs in the realm of the preaching office (Predigamt). That consideration excludes the administration of the sacraments and preaching, insofar as it is public, i.e., addressed to persons other than the members of the household.
Adolf Hoenecke, Evangelical Lutheran Dogmatics, vol. 4, trans. Joel Fredrich, Paul Prange, and Bill Tackmier (Milwaukee: Northwestern Publishing House, 1999), 229-30.