7 From this it may clearly be seen what consequences are to be expected from that false pride which, rejecting our Saviour's Kingship, places man at the summit of all things and declares that human nature must rule supreme. And yet, this supreme rule can neither be attained nor even defined. The rule of Jesus Christ derives its form and its power from Divine Love: a holy and orderly charity is both its foundation and its crown. Its necessary consequences are the strict fulfilment of duty, respect of mutual rights, the estimation of the things of heaven above those of earth, the preference of the love of God to all things. But this supremacy of man, which openly rejects Christ, or at least ignores Him, is entirely founded upon selfishness, knowing neither charity nor self-devotion. Man may indeed be king, through Jesus Christ: but only on condition that he first of all obey God, and diligently seek his rule of life in God's law. By the law of Christ we mean not only the natural precepts of morality and the Ancient Law, all of which Jesus Christ has perfected and crowned by His declaration, explanation and sanction; but also the rest of His doctrine and His own peculiar institutions. Of these the chief is His Church. Indeed whatsoever things Christ has instituted are most fully contained in His Church. Moreover, He willed to perpetuate the office assigned to Him by His Father by means of the ministry of the Church so gloriously founded by Himself. On the one hand He confided to her all the means of men's salvation, on the other He most solemnly commanded men to be subject to her and to obey her diligently, and to follow her even as Himself: "He that heareth you, heareth Me; and he that despiseth you, despiseth Me" (Luke X, 16). Wherefore the law of Christ must be sought in the Church. Christ is man's "Way"; the Church also is his "Way"-Christ of Himself and by His very nature, the Church by His commission and the communication of His power. Hence all who would find salvation apart from the Church, are led astray and strive in vain.
Source: Tametsi Futura Prospicientibus (Vatican.va)