In Lumen Gentium Vatican II defines the Church as the People of God, a term used by some of the Fathers of the Church.
In paragraph 13 we read: “All men are called to be part of this catholic unity of the people of God which in promoting universal peace presages it. And there belong to or are related to it in various ways, the Catholic faithful, all who believe in Christ, and indeed the whole of mankind, for all men are called by the grace of God to salvation.
We have already considered part of paragraph 16: “Finally, those who have not yet received the Gospel are related in various ways to the people of God.(18*) In the first place we must recall the people to whom the testament and the promises were given and from whom Christ was born according to the flesh. On account of their fathers this people remains most dear to God, for God does not repent of the gifts He makes nor of the calls He issues. But the plan of salvation also includes those who acknowledge the Creator. In the first place amongst these there are the Muslims, who, professing to hold the faith of Abraham, along with us adore the one and merciful God, who on the last day will judge mankind. Nor is God far distant from those who in shadows and images seek the unknown God, for it is He who gives to all men life and breath and all things, and as Saviour wills that all men be saved. Those also can attain to salvation who through no fault of their own do not know the Gospel of Christ or His Church, yet sincerely seek God and moved by grace strive by their deeds to do His will as it is known to them through the dictates of conscience. Nor does Divine Providence deny the helps necessary for salvation to those who, without blame on their part, have not yet arrived at an explicit knowledge of God and with His grace strive to live a good life. Whatever good or truth is found amongst them is looked upon by the Church as a preparation for the Gospel. 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. 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”, the Church fosters the missions with care and attention.”
In paragraph 8 we read: “This Church constituted and organized in the world as a society, subsists in the Catholic Church, which is governed by the successors of St. Peter and by the bishops in his communion, although many elements of sanctification and of truth may be found outside of its visible structure, which, as gifts belonging to the Church of Christ, are forces impelling outward catholic unity.”
The Catechism of the Catholic Church teaches: “”Christ bestowed unity on his Church from the beginning. This unity, we believe, subsists in the Catholic Church as something she can never lose, and we hope that it will continue to increase until the end of time.” Christ always gives his Church the gift of unity, but the Church must always pray and work to maintain, reinforce, and perfect the unity that Christ wills for her. This is why Jesus himself prayed at the hour of his Passion, and does not cease praying to his Father, for the unity of his disciples: “That they may all be one. As you, Father, are in me and I am in you, may they also be one in us, . . . so that the world may know that you have sent me.””
Pope Pius IX condemned the propositions (DZ 1716): “In the worship of any religion whatever, men can find the way to eternal salvation.” and (DZ 1717): “We must have at least good hope concerning the eternal salvation of all those who in no wise are in the true Church of Christ.” If there is no salvation outside the Church, how can their be sanctification, since sanctification is a part of salvation?
Pope Boniface VIII infallibly declared on November 18, 1302 (Unam Sanctam, DZ 468): “With Faith urging us we are forced to believe and to hold the one, holy, Catholic Church and that, apostolic, and we firmly believe and simply confess this Church outside which there is no salvation nor remission of sin, …” Vatican II contradicts by stating: many elements of sanctification and of truth may be found outside of its (the Church’s) visible structure, which is in direct contradiction to the infallible statement that there is no remission of sins outside the Church.