God is truth (CCC 215-217; www.vatican.va/archive/ENG0015/__P16.HTM) and therefore can not desire false religions, the existence of which only allows it, because it respects the free will of man.
However, only one and only religion is true, while all others are more or less false.
Diversity in the field of religion is contrary to the Will of God, who revealed the only religion to which he calls absolutely all people inhabited all over the earth:
First, the council professes its belief that God Himself has made known to mankind the way in which men are to serve Him, and thus be saved in Christ and come to blessedness. We believe that this one true religion subsists in the Catholic and Apostolic Church, to which the Lord Jesus committed the duty of spreading it abroad among all men. Thus He spoke to the Apostles: "Go, therefore, and 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 enjoined upon you" (Matt. 28: 19-20). On their part, all men are bound to seek the truth, especially in what concerns God and His Church, and to embrace the truth they come to know, and to hold fast to it ("Dignitatis humanae" 1; www.vatican.va/…/vat-ii_decl_196…).
In order to be faithful to the divine command, "teach all nations" (Matt. 28:19-20), the Catholic Church must work with all urgency and concern "that the word of God be spread abroad and glorified" (2 Thess. 3:1). Hence the Church earnestly begs of its children that, "first of all, supplications, prayers, petitions, acts of thanksgiving be made for all men.... For this is good and agreeable in the sight of God our Savior, who wills that all men be saved and come to the knowledge of the truth" (1 Tim. 2:1-4). In the formation of their consciences, the Christian faithful ought carefully to attend to the sacred and certain doctrine of the Church.(35) For the Church is, by the will of Christ, the teacher of the truth. It is her duty to give utterance to, and authoritatively to teach, that truth which is Christ Himself, and also to declare and confirm by her authority those principles of the moral order which have their origins in human nature itself. Furthermore, let Christians walk in wisdom in the face of those outside, "in the Holy Spirit, in unaffected love, in the word of truth" (2 Cor. 6:6-7), and let them be about their task of spreading the light of life with all confidence(36) and apostolic courage, even to the shedding of their blood ("Dignitatis humanae" 14; www.vatican.va/…/vat-ii_decl_196…).
Incorporated in the Church through baptism, the faithful are destined by the baptismal character for the worship of the Christian religion; reborn as sons of God they must confess before men the faith which they have received from God through the Church (4*). They are more perfectly bound to the Church by the sacrament of Confirmation, and the Holy Spirit endows them with special strength so that they are more strictly obliged to spread and defend the faith, both by word and by deed, as true witnesses of Christ ("Lumen gentium" 11; www.vatican.va/…/vat-ii_const_19…)
This Sacred Council wishes to turn its attention firstly to the Catholic faithful. Basing itself upon Sacred Scripture and Tradition, it teaches that the Church, now sojourning on earth as an exile, is necessary for salvation. Christ, present to us in His Body, which is the Church, is the one Mediator and the unique way of salvation. In explicit terms He Himself affirmed the necessity of faith and baptism(124) and thereby affirmed also the necessity of the Church, for through baptism as through a door men enter the Church. Whosoever, therefore, knowing that the Catholic Church was made necessary by Christ, would refuse to enter or to remain in it, could not be saved ("Lumen gentium" 14; www.vatican.va/…/vat-ii_const_19…).
This missionary activity derives its reason from the will of God, "who wishes all men to be saved and to come to the knowledge of the truth. For there is one God, and one mediator between God and men, Himself a man, Jesus Christ, who gave Himself as a ransom for all" (1 Tim. 2:45), "neither is there salvation in any other" (Acts 4:12). Therefore, all must be converted to Him, made known by the Church's preaching, and all must be incorporated into Him by baptism and into the Church which is His body. For Christ Himself "by stressing in express language the necessity of faith and baptism (cf. Mark 16:16; John 3:5), at the same time confirmed the necessity of the Church, into which men enter by baptism, as by a door. Therefore those men cannot be saved, who though aware that God, through Jesus Christ founded the Church as something necessary, still do not wish to enter into it, or to persevere in it."(17) Therefore though God in ways known to Himself can lead those inculpably ignorant of the Gospel to find that faith without which it is impossible to please Him (Heb. 11:6), yet a necessity lies upon the Church (1 Cor. 9:16), and at the same time a sacred duty, to preach the Gospel. And hence missionary activity today as always retains its power and necessity ("Ad gentes" 7; www.vatican.va/…/vat-ii_decree_1…).
As the Son was sent by the Father,(131) 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".(132) 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.(133) Wherefore she makes the words of the Apostle her own: "Woe to me, if I do not preach the Gospel",(134) 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.(21*) 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)(22*) 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 ("Lumen gentium" 17; www.vatican.va/…/vat-ii_const_19…).
Since Jesus, the Son of God, manifested His charity by laying down His life for us, so too no one has greater love than he who lays down his life for Christ and His brothers.(230) From the earliest times, then, some Christians have been called upon—and some will always be called upon—to give the supreme testimony of this love to all men, but especially to persecutors. The Church, then, considers martyrdom as an exceptional gift and as the fullest proof of love. By martyrdom a disciple is transformed into an image of his Master by freely accepting death for the salvation of the world—as well as his conformity to Christ in the shedding of his blood. Though few are presented such an opportunity, nevertheless all must be prepared to confess Christ before men. They must be prepared to make this profession of faith even in the midst of persecutions, which will never be lacking to the Church, in following the way of the cross ("Lumen gentium" 42; www.vatican.va/…/vat-ii_const_19…).