The Romans have seen something truly unique in the world--mercy shown in the name of religion. However much they may have liked to have seen it in their own history, in reality the true nature of war is that none are spared. By contrast, the shelter offered from the barbarians in the Christian meeting places shows that there is something radically different going on.
Again, we are encouraged to remember that every good thing in this world comes from God through the name of Christ for the benefit of Christians. That blessings fall on pagans as well is simply the overflow of God's kindness and mercy for His people. As Augustine says, "whoever does not see that this is to be attributed to the name of Christ, and to the Christian temper, is blind; whoever sees this and gives no praise, is ungrateful; whoever hinders any one from praising it, is mad." This is one component of the great Christian doctrine of "common grace."
In this common grace mercy, the opportunity to repent is extended to the whole world. This, however, is only one function of good and evil in the world--the larger function is the revelation of human nature. Good and evil alike act upon those who have believed the Gospel in such a way as to improve their character and show their faith, while those who reject the Gospel are made worse by both and confirmed in their sin.