In 1522, Luther preached a sermon entitled “Living as Husband and Wife” (LW, 28: 28), which became a pamplet titled the Estate of Marriage. Here Luther identifies the greatest good in married life, which involves father and mother as apostles, bishops, and priests to their children.
But the greatest good in married life, that which makes all suffering and labour worth while, is that God grants offspring and commands that they be brought up to worship and serve him. In all the world this is the noblest and most precious work, because to God there can be nothing dearer than the salvation of souls. Now since we are all duty bound to suffer death, if need be, that we might bring a single soul to God, you can see how rich the estate of marriage is in good works. God has entrusted to its bosom souls begotten of its own body, on whom it can lavish all manner of Christian works. Most certainly father and mother are apostles, bishops, and priests to their children, for it is they who make them acquainted with the gospel. In short, there is no greater or nobler authority on earth than that of parents over their children, for this authority is both spiritual and temporal. whoever teaches the gospel to another is truly his apostle and bishop. Mitre and staff and great estates indeed produce idols, but teaching the gospel produces apostles and bishops. See therefore how good and great is God’s work and ordinance!
Martin Luther. The Estate of Marriage, 1522. (Translated by Walther I. Brandt).