17 As the Son was sent by the Father, so He too sent the Apostles, saying: "Go, therefore, make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all things whatsoever I have commanded you. And behold I am with you all days even to the consummation of the world". The Church has received this solemn mandate of Christ to proclaim the saving truth from the apostles and must carry it out to the very ends of the earth. Wherefore she makes the words of the Apostle her own: "Woe to me, if I do not preach the Gospel", and continues unceasingly to send heralds of the Gospel until such time as the infant churches are fully established and can themselves continue the work of evangelizing. For the Church is compelled by the Holy Spirit to do her part that God's plan may be fully realized, whereby He has constituted Christ as the source of salvation for the whole world. By the proclamation of the Gospel she prepares her hearers to receive and profess the faith. She gives them the dispositions necessary for baptism, snatches them from the slavery of error and of idols and incorporates them in Christ so that through charity they may grow up into full maturity in Christ. Through her work, whatever good is in the minds and hearts of men, whatever good lies latent in the religious practices and cultures of diverse peoples, is not only saved from destruction but is also cleansed, raised up and perfected unto the glory of God, the confusion of the devil and the happiness of man. The obligation of spreading the faith is imposed on every disciple of Christ, according to his state. Although, however, all the faithful can baptize, the priest alone can complete the building up of the Body in the eucharistic sacrifice. Thus are fulfilled the words of God, spoken through His prophet: "From the rising of the sun until the going down thereof my name is great among the gentiles, and in every place a clean oblation is sacrificed and offered up in my name".(135) In this way the Church both prays and labors in order that the entire world may become the People of God, the Body of the Lord and the Temple of the Holy Spirit, and that in Christ, the Head of all, all honor and glory may be rendered to the Creator and Father of the Universe.
Source: Lumen Gentium (Vatican.va)