The Donatist movement was a heresy which happened during the time of « the great apostasy« . It existed during the 4th century, and like Arianism, descendants of those ideas have now spread over the earth. Like modern-day Arians; known as Jehovah’s Witnesses, Mormons, and other non-believer-in-Jesus-the-God; modern-day Donatists find followers in mixtures of sects, denominations, and churches. They all hold the belief of being the remnant of the true church.
Donatist beliefs came as a response to the evil the Arians were bringing into the Church. Specific of North Africa, Donatists saw that the Church was in chaos, the Eucharist was being desecrated, churches stolen, everything was going wrong. They then developed a doctrine which is still held by several groups in the Church.
His Excellency Felix, Bishop of Aphthongum, was ordained the Deacon Cecilianus bishop to replace His Excellency Mensurius, Bishop of Carthage. The Donatists started a schism because they said that His Excellency Cecilianus was ordained by bishops who were accused of being traditores. Traitors is a descendant of this word. A traditores was someone who delivered the Holy Scriptures to the pagans. The Donatists, being led by a Bishop called Donatus, made a « council » where they « deposed » His Excellency, Bishop Cecilianus, and ordained another to take his place. His Excellency, Bishop Cecilianus ignored them, thereby the Donatists appealed to the Emperor, who, in the year 315 or 316, referred the matter to His Holiness, Pope Melchiades. He and his successor found His Excellency, Bishop Cecilianus innocent not once, nor twice, but three times.
Then the movement was influenced by a second bishop who was called Donatus the Great. He turned the schism into a heresy.
As Saint Alphonsus M. Liguori said on page 24 of The History of Heresies and Their Refutations; or, The Triumph of the Church, Volume I:
In order properly to understand the history of the Donatists, we must separate the schism from the heresy, for they were at first schismatics before they were heretics. Donatus the First was the author of the schism; a second Donatus was the father of the heresy, and he was called by his followers Donatus the Great.
This would be the equivalent of the FSSPX getting a second Lefebvre as the head of their movement, and himself creating a schism and heresy. This is why the FSSPX must be careful not to develop neither a schism nor a heresy, as the Church does not want to have a new massive Donatist movement.
Donatus the Great developed a heresy, of which created many other heresies. This mother of heresies is the belief that Holy Mother Church is composed only of those who are just. The wicked were excluded from it. Like the protestant doctrine of Faith Alone, the Donatist doctrine of Just Alone created many other heresies. Just Alone implicates several layers of understandings, one of which is the ideology of the remnant. The remnant is the belief that the Catholic Church will (or has) fall[en] and the remnants will reconstruct the True Church. The remnant believes that the wicked will fall away from the Church, and that the just alone will remain.
The Donatists of the 300s believed that they were the remnant of the Church, as the Pope in Rome and all Bishops who were not Donatists had « fallen » into heresies and were lost. They also believed several other wrong ideas, one of which was against the validity of the sacraments outside of their sect. Contained in North Africa, the Donatists separated into groups, and the Circumcellionists came. They used violence, which unfortunately became their strong arm, and North Africa, the place where they were, became fire and blood. Suicide became martyr, and killing became giving life. Africa became in flames, and as the Arians did persecutions in the rest of the Roman Empire, so acted the Donatists of North Africa.
It is said that eighty percents (80%), of all Bishops were heretics during these years. It is not hard to believe. In Cartage, the biggest North African city of that time, there was the possibility of having a Roman Catholic Bishop, an Arian bishop, a Donatist bishop, a Circumcellionist bishop, and bishops of other smaller heresies. The Donatist and its daughter heresies lived in Africa until the days of St Gregory the Great, and they paved the way for the ruin of the Church in Africa by the invasion of the Mohammedans.
Most modern-day donatists can fit under today’s belief of the remnant, which is unfortunately strong among some traditionalists groups. The belief that the Catholic Church will fall and only remnants of it will remain is false. The church can be cleansed, but it is not the way of the remnant.
The remnants (the most common form) adheres to a sedevacantist belief, where the Church will be reconstructed after a time of apostasy. The remnant of the true Church will come to Rome and elect a Pope. There are several problems with it, one is that the papacy will disappear of a small time. It cannot as declared by the infallible Council of Vatican I. The second problem is that the structure of the Church will fall. This does not only mean that the Chair of Peter is empty, but that dioceses themselves will fall. Usually this comes with a belief that some few local churches will be left standing. Of course, for the Latin remnants, those are churches are where the Latin Mass is said. Yet the Church cannot fall that way.
For this to happen, all who are « evil » Catholics in their eyes, laity and clergy alike, would have to either die or commit apostasy. To have most of Catholics die implies a kind of rapture, where every bad Catholics are taken away while the just alone remain. This must happen worldwide, and is similar to the protestant invention of the rapture by John Nelson Darby. The other option is that an apostasy happens, where all bad Catholics leave for other religions.
The remnant is partly right on this end, except that it squeeze the time it takes to a very short time. They do not believe in a slow but gradual cleaning of the church, where the old « Spirit of Vatican II » and its generation passes away, where the radicals of a younger generations slowly leave the church, and where the traditional younger generations slowly goes back to its roots. They believe instead in a sudden magical instant, a « poof » moment, where all bad Catholics suddenly leave the Church for any other religions possibles. This include the clergy. While this is possible for some local and very radical areas, it cannot happen on a worldwide scale, as each areas have different levels of faith.
The reality is that the Church will always be, as Saint Alphonsus M. Liguori says:
Then it was that St Augustin […] proved clearer than the noon-day sun that the Church is not composed of the good alone, as the Donatists would have it, but of the good and the bad, as the threshing-floor contains both corn and chaff.
The Church will always have bad Catholics, laity like clergy, especially in the future. Today’s small-c catholics will remain in the church until they die off or they leave, but it will be a slow process. It will take time, efforts, patience, prayers, and sacrifices to endure some of them, but one must see it as a cross they have to bear. One must pick up his cross, and follow Jesus, even if his cross is another Catholic. Carrying that person as a cross might just be what it takes to save their souls.