St. John XXIII witnessed the atrocities of two World Wars and prayed fervently that society would improve. The outlook at the time didn't look promising, but he had hope that the world could change if peace within the family was maintained.
He explained in his encyclical Ad Petri Cathedram that peace within family was the key to peace in the world.
For unless peace, unity, and concord are present in domestic society, how can they exist in civil society?
This harmonious unity which should exist within the family circle rises from the holiness and indissolubility of Christian marriage. It is the basis of much of the order, progress, and prosperity of civil society.
St. John XXIII pointed to the example of the Holy Family at Nazareth for inspiration, and spoke of how their love spread throughout the world.
The charity which burned in the household at Nazareth should be an inspiration for every family. All the Christian virtues should flourish in the family, unity should thrive, and the example of its virtuous living should shine brightly.
However, when the family suffers, the rest of society crumbles, according to St. John XXIII.
We earnestly pray God to prevent any damage to this valuable, beneficial, and necessary union. The Christian family is a sacred institution. If it totters, if the norms which the divine Redeemer laid down for it are rejected or ignored, then the very foundations of the state tremble; civil society stands betrayed and in peril. Everyone suffers.
This view was held by many saints, including St. John Paul II, who did all he could to stress the vital need to preserve the family.
If we desire peace and justice in the world, we need to first look at our own families and work for peace and unity in our own home.