All the errors which are spread around nowadays, and which make believe that there is another way of salvation other than our Lord Jesus Christ and outside the Catholic religion go expressly against the(se) affirmations of the Gospel, and are explicitly against our Lord Jesus Christ.
Documents coming from the Dutch Bishops' Conference speak of ways of salvation in the non-Christian religions. Absurd. There are no means of salvation outside the Catholic religion founded by our Lord Jesus Christ. Outside the Church there is no salvation. It is a dogma of our faith. Why? Because supernatural grace comes only from the Church. Even those graces which might attain adherents of other religions would come from our Lord Jesus Christ, and consequently from His Church, thanks to the prayer of the Church, the mystical spouse of Our Lord who is united to Him and cannot be separated from Him. It is by the intermediary of the Catholic Church that graces are distributed to those who would receive them outside of it.
Undoubtedly, there are souls that are saved and which are not part of the visible structure of the Church, but which belong invisibly to the Church, the mystical body of Christ. The popes have affirmed this. However, undoubtedly this does not occur frequently. The Church must be missionary in order to bring its graces to those who have not received them. If everyone received grace outside the Church, and even if that were by the mediation of the Church, we would not need to be missionaries. It is impossible to be saved by the practice of false religions or by beliefs that are contrary to Church doctrine. It is impossible to be saved by error, by taking a direction opposed to the Holy Ghost, to the Wisdom of God and to the way by which God chose to save us, which is essentially His Incarnation:
Grace and truth came by Jesus Christ. No man hath seen God at any time: the only begotten Son who is in the bosom of the Father, he hath declared him (Jn. 1:17-18).
The mystery of the God-Man is great, clearly; but it is absolutely necessary to meditate on it, and to know the reality, the truth, because this is our faith, our whole life and the life of the world.
Nothing is done in the world that does not relate to Our Lord; it is either for Him or against Him, with Him or without Him. Our Lord is the key to the solution of all the problems. There are none here below that are indifferent to Our Lord. Men try in vain to work without reference to Our Lord, but it is impossible because Our Lord is everywhere.1 He is in everything because He created everything; therefore everything is in His hands. Everything belongs to Him, nothing is outside of Him. Men seek to evade Him, but they cannot because everything is His.
To try to construct human history outside of our Lord Jesus Christ is an absurdity. Our Lord is the center of history. Everything was made by Him and for Him 2 and the only happiness of men and mankind is to be united to Our Lord, to live for God by Jesus Christ, because He is God. He has given us the means; this is why He came. St. John says as much in his first epistle, which is also very beautiful:
That which was from the beginning, which we have heard, which we have seen with our eyes, which we have looked upon and our hands have handled, of the word of life (I Jn. 1:1).
1. By His Divine Nature
2. cf. Col 1:16
Extracts from The Mystery of Jesus, by Archbishop Lefebvre, Angelus Press 2000