Traditionally, Christians engaged interreligious dialogue with the concern that open dialogue was a betrayal of Christian principles. The notion of inclusivism, for which Rahner's Anonymous Christian is the principal Christian model, is "the most popular of interreligious postures.
Anonymous Christianity has been regarded as the one theological idea that most shaped the Second Vatican Council. The long ranging impact of this notion influenced the "ecumenism" of Pope John Paul II and Pope Benedict XVI.
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."
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."
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 "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 highly criticized.
Conservative Christians believe that the notion of Anonymous Christian explicitly contradicts the teachings of Peter, Paul 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 have placed themselves in a state of separation from the Catholic Church since the Second Vatican Council in part because of the Catholic Church's move towards inclusivism. Anonymous Christianity "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.
Karl Rahner did not intend for the term to become derogatory, but rather to explain a mechanism by which non-Christians both present and those who preceded Jesus Christ might be saved.