The schism that separated the Church after the Great Persecution was between the Donatistis and the Catholics and it was a fierce division amongst the early believers of Christianity. Donatists believed that the new Church after the Great Persecution should become a church of holy people, not a group of treacherous degenerates.
In Africa, the Great Persecution was not strongly enforced, so many Christians would easily comply with the mandates against them. However, when the Great Persecution ended those that went along with these performances were then deemed traitors and unfit to be in the Church. They took this to the point that if a sacrament was done by a traitor it was deemed invalid.
They saw themselves as the superior and true Church over the Catholics. A number of other differences became apparent. One example, is the Catholics believed that the sacrament of Reconciliation was something done between the priest and the confessee, but Donatists believed that it was something that should be publicized. In his works Optatus directly opposes the Donatist view of baptism.
He argues that it is does not matter the faith of who physically completes the ceremony of baptism because it is God that blesses it and it is His grace that deems it proper or not. He uses the Bible to support his points as textual evidence. Like in the case of who has a the right to be in the Church he argues that even though Saint Peter denied Jesus three times he was still given the keys to Heaven.
He uses the concept of unity because it was something that both sides of the schism could agree on. Both parties agreed that the Church should be unified but it was under what head and under what ideas that it would be unified under that caused the feuding.
