In The City of God Augustine explains his mission as to disclose the delusions of the pagans who prefer their fictitious gods to Lord, the Founder of the eponymous city and to dictate the divine law to unrighteous for the sake of God’s name. His work is intended to show the difference between the earthly city in which vices are prevailing and which are perishable, as the sack of Rome has proven, and the City of God which is eternal and virtuous. For that end, among other speculations, Augustine turns to the thesis that the proud are resisted by God, while the humble are given His grace. In order to be consistent in his argumentation, the author feels a need to explain why righteous and unrighteous receive divine compassion equally as well as suffer together despite the way they live. It is noted that God promised to visit the transgression with rod and nevertheless never to take away His kindness from those who make mistakes (Augustine). Divine compassion without distinction is supported by the quote that “it was the mercy of Him who daily makes His sun to rise on the evil and on the good, and sends rain on the just and on the unjust” (Matthew 5:45 as quoted in Augustine).
Further, Augustine explains that any scourge is sent to instill patience for the good, while God’s patience to the wicked is given to invite them to repentance. This fact is applied to contrast the City of God and the City on Earth. In earthly city, Augustine states, the wicked and the good suffer together and enjoy mercy together, while in the City of God the righteous will fairly enjoy the welfare they deserve and unrighteous will not.
Finally, there is a beautiful metaphor about gold and chaff, the first glowing in the fire and the latter smoking heavily. Like the oil is divided from the lees when it is squeezed out, the righteous are clarified and purged by affliction, whereas the wicked are ruined and damned.