He wrote in 'Pacem in Terris' that the family is the basic "cell" of human society.
The family has a large role to play in the Catholic Church, but St. John XXIII believed that the family was needed for the functioning of all humanity.
He wrote about this belief in his encyclical Pacem in Terris.
The family, founded upon marriage freely contracted, one and indissoluble, must be regarded as the natural, primary cell of human society. The interests of the family, therefore, must be taken very specially into consideration in social and economic affairs, as well as in the spheres of faith and morals. For all of these have to do with strengthening the family and assisting it in the fulfilment of its mission.
St. John XXIII believed this reality must be reflected in many other parts of civil life, such as the need for a just wage.
A further consequence of man’s personal dignity is his right to engage in economic activities suited to his degree of responsibility. The worker is likewise entitled to a wage that is determined in accordance with the precepts of justice. This needs stressing. The amount a worker receives must be sufficient, in proportion to available funds, to allow him and his family a standard of living consistent with human dignity. Pope Pius XII expressed it in these terms:
“Nature imposes work upon man as a duty, and man has the corresponding natural right to demand that the work he does shall provide him with the means of livelihood for himself and his children. Such is nature’s categorical imperative for the preservation of man.”
The rights of a family also encompass their right to private ownership.
As a further consequence of man’s nature, he has the right to the private ownership of property, including that of productive goods. This, as We have said elsewhere, is “a right which constitutes so efficacious a means of asserting one’s personality and exercising responsibility in every field, and an element of solidity and security for family life, and of greater peace and prosperity in the State.”
St. John XXIII believed, along with every pope since, that when the family is respected, human society can flourish.