Today’s Catechism sections discuss the reality that outside the Church there is no salvation and the missionary activity of the Church. Supporting material comes from the Decree on the Mission Activity of the Church, “Ad Gentes”.

"Outside the Church there is no salvation"

846 How are we to understand this affirmation, often repeated by the Church Fathers?335 Re-formulated positively, it means that all salvation comes from Christ the Head through the Church which is his Body:

Basing itself on Scripture and Tradition, the Council teaches that the Church, a pilgrim now on earth, is necessary for salvation: the one Christ is the mediator and the way of salvation; he is present to us in his body which is the Church. He himself explicitly asserted the necessity of faith and Baptism, and thereby affirmed at the same time the necessity of the Church which men enter through Baptism as through a door. Hence they could not be saved who, knowing that the Catholic Church was founded as necessary by God through Christ, would refuse either to enter it or to remain in it.336

847 This affirmation is not aimed at those who, through no fault of their own, do not know Christ and his Church:

Those who, through no fault of their own, do not know the Gospel of Christ or his Church, but who nevertheless seek God with a sincere heart, and, moved by grace, try in their actions to do his will as they know it through the dictates of their conscience - those too may achieve eternal salvation.337

848 "Although in ways known to himself God can lead those who, through no fault of their own, are ignorant of the Gospel, to that faith without which it is impossible to please him, the Church still has the obligation and also the sacred right to evangelize all men."338

Mission - a requirement of the Church's catholicity

849 The missionary mandate. "Having been divinely sent to the nations that she might be 'the universal sacrament of salvation,' the Church, in obedience to the command of her founder and because it is demanded by her own essential universality, strives to preach the Gospel to all men":339 "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 that I have commanded you; and Lo, I am with you always, until the close of the age."340

850 The origin and purpose of mission. The Lord's missionary mandate is ultimately grounded in the eternal love of the Most Holy Trinity: "The Church on earth is by her nature missionary since, according to the plan of the Father, she has as her origin the mission of the Son and the Holy Spirit."341 The ultimate purpose of mission is none other than to make men share in the communion between the Father and the Son in their Spirit of love.342

851 Missionary motivation. It is from God's love for all men that the Church in every age receives both the obligation and the vigor of her missionary dynamism, "for the love of Christ urges us on."343 Indeed, God "desires all men to be saved and to come to the knowledge of the truth";344 that is, God wills the salvation of everyone through the knowledge of the truth. Salvation is found in the truth. Those who obey the prompting of the Spirit of truth are already on the way of salvation. But the Church, to whom this truth has been entrusted, must go out to meet their desire, so as to bring them the truth. Because she believes in God's universal plan of salvation, the Church must be missionary.

 “Ad Gentes” discusses the missionary activity of the Church:

7. 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.

By means of this activity, the Mystical Body of Christ unceasingly gathers and directs its forces toward its own growth (cf. Eph. 4:11-16). The members of the Church are impelled to carry on such missionary activity by reason of the love with which they love God and by which they desire to share with all men the spiritual goods of both its life and the life to come.

Finally, by means of this missionary activity, God is fully glorified, provided that men fully and consciously accept His work of salvation, which He has accomplished in Christ. In this way and by this means, the plan of God is fulfilled - that plan to which Christ conformed with loving obedience for the glory of the Father who sent Him,(18) that the whole human race might form one people of God and be built up into one temple of the Holy Spirit which, being the expression of brotherly harmony, corresponds with the inmost wishes of all men. And so at last, there will be realized the plan of our Creator who formed man to His own image and likeness, when all who share one human nature, regenerated in Christ through the Holy Spirit and beholding the glory of God, will be able to say with one accord: "Our Father."(19)

Footnotes

335 Cf. Cyprian, Ep. 73.21: PL 3, 1169; De unit.: PL 4, 509-536.
336 LG 14; cf. ⇒ Mk 16:16; ⇒ Jn 3:5[ETML:C/].
337 LG 16; cf. DS 3866-3872.
338 AG 7; cf. ⇒ Heb 11:6; ⇒ 1 Cor 9:16.
339 AG 1; cf. ⇒ Mt 16:15.
340 ⇒ Mt 28:19-20.
341 AG 2.
342 Cf. John Paul II, RMiss 23.
343 ⇒ 2 Cor 5:14; cf. AA 6; RMiss 11.
344 ⇒ 1 Tim 2:4.