48 It is possible to sum up all We have said in one word, "the Kingdom of Christ." For Jesus Christ reigns over the minds of individuals by His teachings, in their hearts by His love, in each one's life by the living according to His law and the imitating of His example. Jesus reigns over the family when it, modeled after the holy ideals of the sacrament of matrimony instituted by Christ, maintains unspotted its true character of sanctuary. In such a sanctuary of love, parental authority is fashioned after the authority of God, the Father, from Whom, as a matter of fact, it originates and after which even it is named. ( Ephesians iii, 15) The obedience of the children imitates that of the Divine Child of Nazareth, and the whole family life is inspired by the sacred ideals of the Holy Family. Finally, Jesus Christ reigns over society when men recognize and reverence the sovereignty of Christ, when they accept the divine origin and control over all social forces, a recognition which is the basis of the right to command for those in authority and of the duty to obey for those who are subjects, a duty which cannot but ennoble all who live up to its demands. Christ reigns where the position in society which He Himself has assigned to His Church is recognized, for He bestowed on the Church the status and the constitution of a society which, by reason of the perfect ends which it is called upon to attain, must be held to be supreme in its own sphere; He also made her the depository and interpreter of His divine teachings, and, by consequence, the teacher and guide of every other society whatsoever, not of course in the sense that she should abstract in the least from their authority, each in its own sphere supreme, but that she should really perfect their authority, just as divine grace perfects human nature, and should give to them the assistance necessary for men to attain their true final end, eternal happiness, and by that very fact make them the more deserving and certain promoters of their happiness here below.
Source: Ubi Arcano Dei Consilio (Vatican.va)