In the other thread on modernism, that got derailed, there were a couple dangling issues. One was enunciated as so:
Show me in Nostra Aetate where there is a call to" free them from error and all contamination " and to perfect and complete them by Christian revelation.
And the other was that there is now a fear of calling to convert–given the implication that finding common ground and building from there is opposed to enunciating the need for conversion or that affirming what is good is done for its own end, as opposed to finding the fertile ground for the Gospel.
Nostra Aetate is not dealing with this issue, but rather with collaboration and interaction in pluralistic societies. As John Paul II said in his encyclical on the mssions (see below), inter-religious dialogue is not the same as evangelization, nor should it be a replacement for it. The Second Vatican Council’s decree on the Missions, Ad Gentes, deals with the topic at hand. Here are some examples:
"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.”
“They must be acquainted with this culture; they must heal it and preserve it; they must develop it in accordance with modern conditions, and finally perfect it in Christ, so that the Faith of Christ and the life of the Church are no longer foreign to the society in which they live, but begin to permeate and to transform it.”
“Missionary activity is nothing else and nothing less than an epiphany, or a manifesting of God’s decree, and its fulfillment in the world and in world history, in the course of which God, by means of mission, manifestly works out the history of salvation. By the preaching of the word and by the celebration of the sacraments, the center and summit of which is the most holy Eucharist, He brings about the presence of Christ, the author of salvation. But whatever truth and grace are to be found among the nations, as a sort of secret presence of God, He frees from all taint of evil and restores to Christ its maker, who overthrows the devil’s domain and wards off the manifold malice of vice. And so, whatever good is found to be sown in the hearts and minds of men, or in the rites and cultures peculiar to various peoples, not only is not lost, but is healed, uplifted, and perfected for the glory of God, the shame of the demon, and the bliss of men.”
And also Lumen Gentium
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.
Whatever good or truth is found amongst them is looked upon by the Church as a preparation for the Gospel.(20*) She knows that it is given by Him who enlightens all men so that they may finally have life. But often men, deceived by the Evil One, have become vain in their reasonings and have exchanged the truth of God for a lie, serving the creature rather than the Creator.(129) Or some there are who, living and dying in this world without God, are exposed to final despair. Wherefore to promote the glory of God and procure the salvation of all of these, and mindful of the command of the Lord, “Preach the Gospel to every creature”,(130) the Church fosters the missions with care and attention.
And also Gaudium et Spes
This love and good will, to be sure, must in no way render us indifferent to truth and goodness. Indeed love itself impels the disciples of Christ to speak the saving truth to all men. But it is necessary to distinguish between error, which always merits repudiation, and the person in error, who never loses the dignity of being a person even when he is flawed by false or inadequate religious notions. God alone is the judge and searcher of hearts; for that reason He forbids us to make judgments about the internal guilt of anyone.
But at the same time, the Church, sent to all peoples of every time andplace, is not bound exclusively and indissolubly to any race or nation,any particular way of life or any customary way of life recent orancient. Faithful to her own tradition and at the same time conscious of her universal mission, she can enter into communion with the various civilizations, to their enrichment and the enrichment of the Churchherself.The Gospel of Christ constantly renews the life and culture of fallenman; it combats and removes the errors and evils resulting from thepermanent allurement of sin. It never ceases to purify and elevate themorality of peoples. By riches coming from above, it makes fruitful, asit were from within, the spiritual qualities and traditions of everypeople and of every age. It strengthens, perfects and restores them in Christ.
And recent Pontiffs have said the same. I was going to provide more and more passages, but there were too many and they were too long, so I will provide links to the entirety of the texts here. All emphasize the need for preaching the Gospel and conversion as necessary for the salvation of souls, rejecting ideas that conversion and missionary activity are not necessary or encouraged and that the Gospel perfects other religions from their errors.
Pope Paul VI
Evangelii Nuntiandi (On Evangelization in the Modern World) December 8, 1975 [Apostolic Exhortation]
John Paul II
Redemptoris Missio (On the Permanent Validity of the Church’s Missionary Mandate) December 7, 1990
Ecclesia in Africa (On the Church in Africa) September 14, 1995 [Apostolic Exhortation]
Ecclesia in Asia (On the Church in Asia) November 6, 1999 [Apostolic Exhortation]
Dominus Iesus (On the Unicity and Salvific Universality of Jesus Christ and the Church) - from the Congregation for the Doctrine of the Faith, August 6, 2000