This view of the nature of government, and the Church’s relationship to it, is laid out more fully in Leo’s encyclical Immortale Dei (“On the Christian Constitution of the State). The third paragraph of that document sums it up nicely:
It is not difficult to determine what would be the form and character of the State were it governed according to the principles of Christian philosophy. Man's natural instinct moves him to live in civil society, for he cannot, if dwelling apart, provide himself with the necessary requirements of life, nor procure the means of developing his mental and moral faculties. Hence it is divinely ordained that he should lead his life, be it family, social, or civil, with his fellow-men, amongst whom alone his several wants can be adequately supplied. But as no society can hold together unless someone be over all, directing all to strive earnestly for the common good, every civilized community must have a ruling authority, and this authority, no less than society itself, has its source in nature, and has consequently God for its author. Hence it follows that all public power must proceed from God. For God alone is the true and supreme Lord of the world. Everything without exception must be subject to Him, and must serve Him, so that whosoever holds the right to govern, holds it from one sole and single source, namely God, the Sovereign Ruler of all. “There is no power but from God.”Thus, both the Church and the State ultimately serve God. Not only that, but some kind of State (i.e., governing structure) is necessary and natural if individuals and society as a whole are to prosper.
Once the case for the Church and her agencies has been made, the encyclical goes on to delineate the State’s legitimate role in ordering society. First, it is pointed out that it is in the State’s best interest to see to it that its laws and institutions allow people to live good lives, as this will promote peace and the common good. In particular, the State should see to it that the rights of the working class are protected, since they make up the bulk of society and their labor serves the whole of society. In other words, it would be foolish and impractical to allow workers to be victimized by their wealthy employers, because without a healthy working class everything would grind to a halt.
Still, the State’s job seems to be, not to interfere in and manage the daily lives of its citizens, but to see that justice prevails in public and private matters. That is, it should stand by in case things go wrong, or appear to be about to go wrong, and to intervene only when necessary to avoid a breakdown (such as work stoppages or riots) in the normal operations of society and industry, and only until peace and justice have been restored, which would include addressing the causes of such disturbances -- e.g., the lamentable conditions that drive workers to strike. Bearing in mind the dangerous ideas put forth by Socialists, Leo also addresses specifically acts of class warfare that would violate justice, such as workers' seizing the property of the owners of capital, as well as greedy capitalists' treatment of workers as wage slaves in order to wring the maximum profit from their labors -- either of these would be grossly unjust, and the State should guard against them.
However, the State’s role is also to safeguard the good of the individual, even when the individual might not want it to do so, much as a father must sometimes do things for his child’s good, even if the child does not recognize that action as good. So, for instance, a worker desperate to earn money might agree to poor wages, excessively long hours, or bad working conditions, but the State should not allow it. It is interesting that Leo claims that the State should safeguard not only the material well-being of its citizens, but also their moral well-being, by making sure that workers have time not only to recuperate from their labors, but also to spend time with their families and to worship. This is in accord with the Church's view that the State “no less than society itself, has its source in nature, and has consequently God for its author.”