3 Seeing therefore, too, these cases occur in persecutions more than at other times, as there is then among us more of proving or rejecting, more of abusing or punishing, it must be that their general occurrence is permitted or commanded by Him at whose will they happen even partially; by Him, I mean, who says, “I am He who make peace and create evil,” — that is, war, for that is the antithesis of peace. But what other war has our peace than persecution? If in its issues persecution emphatically brings either life or death, either wounds or healing, you have the author, too, of this.
“I will smite and heal, I will make alive and put to death.” “I will burn them,” He says, “as gold is burned; and I will try them,” He says, “as silver is tried,” for when the flame of persecution is consuming us, then the steadfastness of our faith is proved. These will be the fiery darts of the devil, by which faith gets a ministry of burning and kindling; yet by the will of God. As to this I know not who can doubt, unless it be persons with frivolous and frigid faith, which seizes upon those who with trembling assemble together in the church.
For you say, seeing we assemble without order, and assemble at the same time, and flock in large numbers to the church, the heathen are led to make inquiry about us, and we are alarmed lest we awaken their anxieties. Do you not know that God is Lord of all? And if it is God's will, then you shall suffer persecution; but if it is not, the heathen will be still. Believe it most surely, if indeed you believe in that God without whose will not even the sparrow, a penny can buy, falls to the ground. But we, I think, are better than many sparrows.
Source: De Fuga in Persecutione (New Advent)