I. “Catholic”?
II. Who is Catholic?
III. What are the true teachings of the Catholic Faith?
IV. Is it necessary to be Catholic to be saved?
V. Can the Church’s Dogmatic teaching change?
VI. What must we do to be truly called Catholic?

A clear definition of the Church was given to us by the great Jesuit and Doctor of the Church Saint Robert Bellarmine:

“A body of men united together by the profession of the same Christian Faith, and by participation in the same sacraments, under the governance of lawful pastors, more especially of the Roman Pontiff, the sole vicar of Christ on earth.” (Coetus hominum ejusdem christianæ fidei professione, et eorumdem sacramentorum communione colligatus, sub regimine legitimorum pastorum et præcipue unius Christi in Terris vicarii Romani Pontificis.) (De Eccl., III, ii, 9.)

To this can be added:

“See that you all follow the bishop, even as Jesus Christ does the Father, and the presbytery as you would the apostles; and reverence the deacons, as being the institution of God. Let no man do anything connected with the Church without the bishop. Let that be deemed a proper Eucharist, which is [administered] either by the bishop, or by one to whom he has entrusted it. Wherever the bishop shall appear, there let the multitude [of the people] also be; even as, wherever Jesus Christ is, there is the Catholic Church.” -Saint Ignatius of Antioch, Father of the Church, Epistle to the Smyrnaeans #8, (50-117AD)

For a more fleshed out explanation we can turn to the Roman Catechism, which is still the official manual for Catholic Priests to use for catechizing the faithful, and was commissioned by Pope Saint Pius V to be a faithful explanation of the infallible decrees of the Council of Trent, and which was edited by the great Saint Charles Borromeo to whom we also owe for the modern Seminary system:

The Parts of the Church

These things having been explained, it will be necessary to enumerate the several component parts of the Church, and to point out their difference, in order that the faithful may the better comprehend the nature, properties, gifts, and graces of God’s beloved Church, and by reason of them unceasingly praise the most holy name of God.

The Church consists principally of two parts, the one called the Church triumphant; the other, the Church militant. The Church triumphant is that most glorious and happy assemblage of blessed spirits, and of those who have triumphed over the world, the flesh, and the iniquity of Satan, and are now exempt and safe from the troubles of this life and enjoy everlasting bliss. The Church militant is the society of all the faithful still dwelling on earth. It is called militant, because it wages eternal war with those implacable enemies, the world, the flesh and the devil.

We are not, however, to infer that there are two Churches. The Church triumphant and the Church militant are two constituent parts of one Church; one part going before, and now in the possession of its heavenly country; the other, following every day, until at length, united with our Saviour, it shall repose in endless felicity.

The Members Of The Church Militant

The Church militant is composed of two classes of persons, the good and the bad, both professing the same faith and partaking of the same Sacraments, yet differing in their manner of life and morality.

The good are those who are linked together not only by the profession of the same faith, and the participation of the same Sacraments, but also by the spirit of grace and the bond of charity. Of these St. Paul says: The Lord knoweth who are his. Who they are that compose this class we also may remotely conjecture, but we can by no means pronounce with certainty. Hence Christ the Saviour does not speak of this portion of His Church when He refers us to the Church and commands us to hear and to obey her. As this part of the Church is unknown, how could we ascertain with certainty whose decision to recur to, whose authority to obey?

The Church, therefore, as the Scriptures and the writings of the Saints testify, includes within her fold the good and the bad; and it was in this sense that St. Paul spoke of one body and one spirit. Thus understood, the Church is known and is compared to a city built on a mountain, and visible from every side. As all must yield obedience to her authority, it is necessary that she may be known by all.

That the Church is composed of the good and the bad we learn from many parables contained in the Gospel. Thus, the kingdom of heaven, that is, the Church militant, is compared to a net cast into the sea, to a field in which tares were sown with the good grain, to a threshing floor on which the grain is mixed up with the chaff, and also to ten virgins, some of whom were wise, and some foolish. And long before, we trace a figure and resemblance of this Church in the ark of Noah, which contained not only clean, but also unclean animals.

But although the Catholic faith uniformly and truly teaches that the good and the bad belong to the Church, yet the same faith declares that the condition of both is very different. The wicked are contained in the Church, as the chaff is mingled with the grain on the threshing floor, or as dead members sometimes remain attached to a living body.

Those Who Are Not Members Of The Church

Hence there are but three classes of persons excluded from the Church’s pale: infidels, heretics and schismatics, and excommunicated persons. Infidels are outside the Church because they never belonged to, and never knew the Church, and were never made partakers of any of her Sacraments. Heretics and schismatics are excluded from the Church, because they have separated from her and belong to her only as deserters belong to the army from which they have deserted. It is not, however, to be denied that they are still subject to the jurisdiction of the Church, inasmuch as they may be called before her tribunals, punished and anathematised. Finally, excommunicated persons are not members of the Church, because they have been cut off by her sentence from the number of her children and belong not to her communion until they repent.

But with regard to the rest, however wicked and evil they may be, it is certain that they still belong to the Church: Of this the faithful are frequently to be reminded, in order to be convinced that, were even the lives of her ministers debased by crime, they are still within the Church, and therefore lose nothing of their power.