Similarly, accidental differences in ceremonial forms do not in the least interfere with essential unity of worship, which is to be regarded primarily and principally in the celebration of the same sacrifice and in the reception of the same sacraments. All are expressive of the one doctrine and subject to the same authority. These words of Christ are expressive of the closest unity. St. Paul likewise insists on the unity of the Church. Such declarations as these coming from the great Apostle are clear evidence of the essential unity which must be characteristic of the true Christian Church.
Tradition is unanimous to the same effect.
Whenever heresy threatened to invade the Church, the Fathers rose up against it as an essential evil. The same contention was upheld by Clement of Alexandria and by Origen, who said that outside the one visible Church none could be saved. Many more testimonies of unity might be adduced from Saints Jerome, Augustine, Chrysostom, and the other Fathers, but their teachings are only too well known. The long list of councils, the history and treatment of heretics and heresies in every century show beyond doubt that unity of doctrine of cult, and of authority, has always been regarded as an essential and visible mark of the true Christian Church. As shown above, it was the intention of Christ that His Church should be one, and that, not in any accidental internal way, but essentially and visibly.