It was not me who said it, it was the Catholic Dictionary by Donald Attwater. IT IS MEANINGLESS IN THE WAY THE WORLD USES IT!, not the Church! Here is the definition again:
CHRISTIAN. A name first given to the followers of our Lord at Antioch (Acts xi, 26). Since the rise of Protestantism the name has been used in so many different senses as to have become almost meaningless: it may indicate a Catholic or a Unitarian, or even be applied to an infidel who displays some virtue which is associated with Christ. It may reasonably be applied to the members of all the ancient churches whether in communion with the Holy See or not, and to those Protestants who profess, explicitly -or implicitly, the Nicean creed in its traditional Interpretation. The Church puts no definite official meaning on the word, as she does on Catholic. (Catholic Dictionary, Donald Attwater, 1958, TAN Books)
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The term Christian to Church Fathers, Bellarmine, , AND PIUS IX :
Those who go off to heretics, and all who leave the Church for heresy, abandon the name of Christ. Those who call these men "Christians" are in grievous error, since they neither understand Scripture at all nor the faith which it contains. St Athanasius ("Discourse Against the Arians", Bk. I, ch.1,no.1, pg 26:11)
In name only is Christ found among certain heretics who want to be called Christians. In reality, He is no longer among them. (St. Augustine)
He who falls away from the doctrine and faith of the Catholic Church would not be, nor would even be called, a Christian. (St. Athanasius)
]All true Christians are members of the Church. (St. John Eudes)
Whosoever and whatsoever he might be, he who is not in Christ's Church is no Christian! (St. Cyprian)
A manifest heretic is not a Christian, as is clearly taught by St. Cyprian, St. Athanasius, St. Augustine, St. Jerome, and others. (St Robert Bellarmine)
Pope Pius IX, Etsi multa (#25), November 21, 1873: Therefore the holy martyr Cyprian, writing about schism, denied to the pseudo-bishop Novatian even the title of Christian, on the grounds that he was cut off and separated from the Church of Christ. Whoever he is, he says, and whatever sort he is, he is not a Christian who is not in the Church of Christ.
From: Mystici Corporis Christi, by Pope Pius XII (and First Vatican council):
The true Church of Jesus Christ ...is the One, Holy, Catholic, Apostolic and Roman Church
.........."or the union of Christians can only be promoted by promoting the return to the one true Church of Christ."
Well?