"When parents achieve a mastery of themselves and not just their physical environments, this lesson too is not lost on their children. Self-mastery, like endurance, is a behavior which is incontrovertibly personal. It cannot be done to someone from the outside. But, when there are examples of it around us, we tend to pick up on it and make it our own. Thus, there is a generational impact. The children of self-mastering parents -- who become self-mastering adults themselves -- are then more likely to possess healthy attitudes for confronting problems and dilemmas, and are less likely to resort to ... socially harmful conduct."
— Rev. Msgr. Robert Batule on why parents who wish their children to learn chastity ought to demonstrate it in their own marriage, from his essay "Humanae Vitae the Nexus of Personal and Social Morality." Read the whole piece.