https://infogalactic.com/info/Portal:Catholicism
C. Th. XVI.i.2. IT IS Our will that all the peoples who are ruled by the administration of Our Clemency shall practice that religion which the divine Peter the Apostle transmitted to the Romans, as the religion which he introduced makes clear even unto this day. It is evident that this is the religion that is followed by the Pontiff Damasus and by Peter, Bishop of Alexandria, a man of apostolic sanctity; that is, according to the apostolic discipline and the evangelic doctrine, we shall believe in the single Deity of the Father, the Son, and the Holy Spirit, under the concept of equal majesty and of the Holy Trinity.
We command that those persons who follow this rule shall embrace the name of Catholic Christians. The rest, however, whom We adjudge demented and insane, shall sustain the infamy of heretical dogmas, their meeting places shall not receive the name of churches, and they shall be smitten first by divine vengeance and secondly by the retribution of Our own initiative, which We shall assume in accordance with the divine judgment (28 February 380).
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OK, but what about those who are not members of the Perfect Society, are they Christians?
Pope Pius XII
To be Christian one must be Roman. One must recognize the oneness of Christ’s Church that is governed by one successor of the Prince of the Apostles who is the Bishop of Rome, Christ’s Vicar on earth.
If anyone does not follow Christ as a member of the Catholic Church He established, how can anyone justify calling him Christian?
https://catholiccandle.neocities.org/faith/heretics-are-not-christians.html