Anonymous Christian is the controversial notion introduced by the Jesuit theologian Karl Rahner (1904–1984) that declares that people who have never heard the Christian Gospel might be saved through Christ. Non-Christians could have "in [their] basic orientation and fundamental decision," Rahner wrote, "accepted the salvific grace of God, through Christ, although [they] may never have heard of the Christian revelation."
Anonymous Christianity means that a person lives in the grace of God and attains salvation outside of explicitly constituted Christianity — Let us say, a Buddhist monk — who, because he follows his conscience, attains salvation and lives in the grace of God; of him I must say that he is an anonymous Christian; if not, I would have to presuppose that there is a genuine path to salvation that really attains that goal, but that simply has nothing to do with Jesus Christ. But I cannot do that. And so, if I hold if everyone depends upon Jesus Christ for salvation, and if at the same time I hold that many live in the world who have not expressly recognized Jesus Christ, then there remains in my opinion nothing else but to take up this postulate of an anonymous Christianity. 
According to Rahner, a person could explicitly deny Christianity, but in reality "existentially is committed to those values which for the Christian are concretized in God."
Vatican II and Catholicism
Karl Rahner's concept of Anonymous Christian was one of the most influential theological ideals to affect the Second Vatican Council.
In Lumen gentium, the council fathers stated: "Those also can attain to everlasting 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." They went on to write, in Gaudium et spes, "Since Christ died for all men, and since the ultimate vocation of man is in fact one, and divine, we ought to believe that the Holy Spirit in a manner known only to God offers to every man the possibility of being associated with this paschal mystery."
The Catechism of the Catholic Church teaches, "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." 
However, Lumen gentium states that those who have been given knowledge of Christ, and fail to act "... could not be saved."
Pope Benedict XVI
Before becoming Pope Benedict XVI, Joseph Cardinal Ratzinger headed the Congregation for the Doctrine of the Faith. In this role, he issued, with the approval of Pope John Paul II, a document called Dominus Iesus. This document asserts the supremacy of the Catholic Church, while reiterating the Catholic Church's acceptance of a modified form of "anonymous Christianity".
"Nevertheless, God, who desires to call all peoples to himself in Christ and to communicate to them the fullness of his revelation and love, "does not fail to make himself present in many ways, not only to individuals, but also to entire peoples through their spiritual riches, of which their religions are the main and essential expression even when they contain ‘gaps, insufficiencies and errors'". Therefore, the sacred books of other religions, which in actual fact direct and nourish the existence of their followers, receive from the mystery of Christ the elements of goodness and grace which they contain." (I, 8)
"Theology today, in its reflection on the existence of other religious experiences and on their meaning in God's salvific plan, is invited to explore if and in what way the historical figures and positive elements of these religions may fall within the divine plan of salvation. In this undertaking, theological research has a vast field of work under the guidance of the Church's Magisterium. The Second Vatican Council, in fact, has stated that: "the unique mediation of the Redeemer does not exclude, but rather gives rise to a manifold cooperation which is but a participation in this one source"." (III, 14)
"With respect to the way in which the salvific grace of God — which is always given by means of Christ in the Spirit and has a mysterious relationship to the Church — comes to individual non-Christians, the Second Vatican Council limited itself to the statement that God bestows it "in ways known to himself"." (VI, 21)
The notion of Anonymous Christian has been criticized.
Conservative Protestant Christians generally believe that the notion of Anonymous Christian explicitly contradicts the teachings of Saint Peter, Paul the Apostle and other Apostles. For example, Acts 4:12, "there is salvation in no one else; for there is no other name under heaven that has been given among men, by which we must be saved." This group of Christians believe in "Christian exclusivism—the view that biblical Christianity is true, and that other religious systems are false." Some Catholic groups, such as the Society of St. Pius X, though not in a state of schism, have long battled against the rise of liberalism, modernism, and attitudes of inclusiveness in the Catholic Church, particularly since the Second Vatican Council. Anonymous Christianity, the Society writes, "is a very grave doctrinal error because it declares personal justification as being already realized for every man without any participation of his will or free choice and, so, without any need of his conversion, faith, baptism or works. Redemption is guaranteed to all, as if sanctifying grace were ontologically present in each man just because he is man."
Liberal Christians condemn the notion because, as Hans Küng put it, "It would be impossible to find anywhere in the world a sincere Jew, Muslim or atheist who would not regard the assertion that he is an 'anonymous Christian' as presumptuous". John Hick states that this notion is paternalistic because it is "honorary status granted unilaterally to people who have not expressed any desire for it." Hick further rejects the notion because the majority of people are born into non-Christian families. Anonymous Christianity, per this group, denigrates the beliefs of others by supposing that they are really Christians without realizing it.
- Clinton, Stephen. Peter, Paul, and the Anonymous Christian: A Response to The Mission Theology of Rahner and Vatican II October, 1998 The Orlando Institute, Leadership Forum November, 1998 Evangelical Theological Society
- Davies, William David; Davies, W. D.; Allison, Dale C. (1997). Matthew: Volume 3: 19-28. A&C Black. p. 423. ISBN 9780567085184.
Rather did he hold the position stated in the Apocalypse of Sedrach: 'there are nations which have no law, yet fulfill the law; they are not baptized, but my divine Spirit enters them and they are converted to my baptism, and I receive them with my righteous ones in the bosom of Abraham. [There were rabbis who taught that righteous heathen would be saved: t. Sanh. 13.2; b. Sanh. 105a. Recall also Paul's thoughts in Rom 2.14-16: Gentiles who do the law written on their hearts may have good consciences on the last day.] The context, however, does not explicitly teach two judgements; and we are not persuaded that 'the least' are to be identified with Christians (see below). Further, we have little doubt before Matthew, the scene concerned all humanity. At the same time, 25.31-46 may very well imply that Matthew thought salvation possible for those outside the church. We are reminded of Karl Rahner's so-called 'anonymous Christian'.
- Robbins, Jerry. A Reader’s Guide to Interreligious Dialogue Lutheran Campus Center, Morgantown, West Virginia. 1989 by Word & World, Luther Seminary, St. Paul, MN.
- Karl Rahner in Dialogue, p. 135
- Moffitt, John. Interreligious Encounter and the Problem of Salvation Christian Century, November 17, 1976, pp. 1001–1007
- Article 847 of The Catechism of the Catholic Church
- DOMINUS IESUS ON THE UNICITY AND SALVIFIC UNIVERSALITY OF JESUS CHRIST AND THE CHURCH
- Rood, Rick. The Christian Attitude Toward Non-Christian Religions Probe Ministries
- Mershon, Brian (April 10, 2007). "Cardinal Castrillón: SSPX not in schism". Renew America.
- Errors of Vatican II Society of St Pius X, Australian District. Si Si No No May 2003 No. 52
- Karl Rahner's Arguments for Inclusivism St John in the Wilderness
- Markham, Ian. The Dialogue Industry December 2004. Hartford Seminary
- Weigel, George. The Century after Rahner Catholic Culture