8 Missionary activity is closely bound up even with human nature itself and its aspirations. For by manifesting Christ the Church reveals to men the real truth about their condition and their whole calling, since Christ is the source and model of that redeemed humanity, imbued with brotherly love, sincerity and a peaceful spirit, to which they all aspire. Christ and the Church, which bears witness to Him by preaching the Gospel, transcend every peculiarity of race or nation and therefore cannot be considered foreign anywhere or to anybody. Christ Himself is the way and the truth, which the preaching of the Gospel opens to all in proclaiming in the hearing of all these words of Christ: "Repent, and believe the Gospel" (Mark 1:15). Now, since he who does not believe is already judged (cf. John 3:18), the words of Christ are at one and the same time words of judgment and of grace, of death and of life. For it is only by putting to death what is old that we are able to approach the newness of life. This is true first of all about persons, but it holds also for the various goods of this world which bear the mark both of man's sin and of God's blessing: "For all have sinned and have need of the glory of God" (Rom. 3:23). No one is freed from sin by himself and by his own power, no one is raised above himself, no one is completely rid of his sickness or his solitude or his servitude. On the contrary, all stand in need of Christ, their model, their mentor, their liberator, their Savior, their source of life. The Gospel has truly been a leaven of liberty and progress in human history, even in the temporal sphere, and always proves itself a leaven of brotherhood, of unity and of peace. Not without cause is Christ hailed by the faithful as "the expected of the nations, and their Savior."
Source: Ad Gentes (Vatican.va)