In the early fourth century AD, the church was experiencing another siege of persecution. In moments of weakness or under actual torture, many presbyters handed over copies of scripture, renounced the faith, and in many instances even denounced other Christians. These former presbyters were called traditori. 
The majority of the church felt that if a traditor wished to return to the church, he could after a period of penance lasting a few weeks to several decades, and rebaptism.  Donatus, bishop of Caesa Nigraee, disagreed with the majority opinion. He preached his opinion and gained a sizeable following.
Things came to a head in 311 A.D. when Caecilian of Cathrage was consecrated bishop. One of the three officiating bishops,  Felix of Aptunga, had been a traditor. Donatus and seventy bishops withdrew their fellowship from the whole church, formed their own synod and declared the consecration null and void.
Emboldened by their own hubris, in 315 A.D. the donatists declared
- “The whole catholic church was lost” (apostate) because sinners were allowed to officiate at the altars
- That they themselves were the “only true church”
- That, as the “only true Church,” they could not pray in the same building with apostates
- They could not recognize any sacrament performed by “apostates” (this included marriage, baptism, Eucharist, holy orders) nor
- receive any sacraments from the hands of apostates
- be in the same building when apostate rites were being performed
- That some sins were worse than other sins
- That “committing” these super-sins forever barred persons from ordained ministry. (Naturally, Donatists leaders got to pick the 'super-sins')
Although repudiated by every council of the Church, it was not until the seventh century that the movement officially died. But Donatism is the heresy that just will not die. Like a weed in a formal garden, periodically donatism would raise deceptive bloom. During the reformation, Donatism made an appearance in the form of the Puritans who attempted to “take over” the Church of England.
Now that you know much more than you ever wanted to know, (but trust me this doesn’t scratch the surface!) the question you are asking is, “what does all this mean to me?” The answer is threefold:
- Donatistism sets up a small group to be absolute judge of all others
- Donatists proclaim that as the “only true church” they have the exclusive interpretation of “orthodox” teaching, scriptural interpretation, sacramental validity, sin, and an individual’s worthiness (it doesn’t matter if “you” believe that you are a Christian—they will tell you if you are or not)
- Donatism is at work in the church once again
Logically, Donatism is an impossible theological position to defend because no one is morally pure. . Therefore, by donatisim’s own rules, there are no valid sacraments or ministers – not even in their inner circle. Also,
Anglicanism has always condemned Donatism. According to our catechism, Sacraments are:
[A]n outward and visible sign of an inward and spiritual grace given unto us; ordained by Christ himself, as a means whereby we receive the same , and a pledge to assure us thereof. BCB 1928. p. 581 
[O]utward and visible signs of inward and spiritual grace, given by Christ as sure and certain means by which we receive that grace.”
BCP 1979, p. 857
Notice the important part of the catechism’s explanation – we receive Christ’s grace, not the presbyter’s grace. Think of that Grace as pitcher of water. One may pour that water into an old cracked glass or a golden cup. The water is still water regardless of which vessel from which one drinks.
What makes Donatism morally dangerous is that it puts an impediment between God’s grace and us. It says that God is constrained by humans. It says that God can be God only when the human medium is good enough. It says “I know better than God does. It says that God cannot overcome sin.
Thanks be to God, all of that was repudiated on a cross outside of
How to spot a modern Anglican donatist (neo-donatist):
- “The Episcopal and Anglican Church of
is apostate!” Canada
- “Thank goodness there are still real Anglicans left”
- “He/she is [insert term] so I can’t take communion from him/her
- “If the bible says it, that settles it.” (Always said as a conversation stopper.)
- “You don’t respect the authority of the bible.”
- “If you were a real Christian, you would see that you are wrong.”
- “The faith once delivered to the saints” is a favourite quote of Donatists
- An unhealthy obsession about certain issues and silence on other issues the bible condemns.
- A propensity to use the Old Testament purity laws to govern the Christian church.(but very selective about which purity laws are still enforceable)