Despite Augustine's long and dominating shadow over 1,500 years of Western church history, his central ideas have not been universally accepted or uniformly interpreted. The Eastern Orthodox regard some of Augustine's key ideas as pernicious, if not heretical. Anabaptists have rejected much of his theology, while Protestants in general claim selected teachings and ignore others.
Nonetheless, Augustine is widely regarded as the church's most influential philosopher and theologian. His five central ideas were forged in the heat of theological conflict, and they remain controversial today:
1. The nature and source of evil.
2. The nature of the church and its sacraments.
3. Original sin.
4. The relationship of grace and free will.
Augustine refined each of these doctrines as he battled what he believed were heresies, or at least false worldviews: a dualistic "cult" known as the Manichees, a Christian sect in North Africa known as the Donatists, and the beliefs of a British monk named Pelagius and his followers. Augustine's distinctive teachings are essentially answers to these theological enemies.
One of the most pressing theological problems in Augustine's time was how to justify belief in an omnipotent and perfectly good Creator when sin and evil were obviously deeply woven into the created beings.
The Manichees taught that two eternal beings control the universe, one of them good and the other evil. Even if the all-good deity is superior, they argued, it cannot at present conquer or control the evil one. The Manichees also taught that evil is intrinsically associated with matter and that only spirit is good. Thus, the good deity created spirits but not matter.