Humanae Vitae §26

²⁶ Among the fruits that ripen if the law of God be resolutely obeyed, the most precious is certainly this, that married couples themselves will often desire to communicate their own experience to others. Thus it comes about that in the fullness of the lay vocation will be included a novel and outstanding form of the apostolate by which, like ministering to like, married couples themselves by the leadership they offer will become apostles to other married couples. And surely among all the forms of the Christian apostolate it is hard to think of one more opportune for the present time. (38)