But if all the Romans, according to the supposition of Celsus, embrace the Christian faith, they will, when they pray, overcome their enemies; or rather, they will not war at all, being guarded by that divine power which promised to save five entire cities for the sake of fifty just persons. For men of God are assuredly the salt of the earth: they preserve the order of the world; and society is held together as long as the salt is uncorrupted: for “if the salt have lost its savour, it is neither fit for the land nor for the dunghill; but it shall be cast out, and trodden under foot of men.
He that has ears, let him hear” the meaning of these words. When God gives to the tempter permission to persecute us, then we suffer persecution; and when God wishes us to be free from suffering, even in the midst of a world that hates us, we enjoy a wonderful peace, trusting in the protection of Him who said, “Be of good cheer, I have overcome the world.” And truly He has overcome the world. Wherefore the world prevails only so long as it is the pleasure of Him who received from the Father power to overcome the world; and from His victory we take courage.
Should He even wish us again to contend and struggle for our religion, let the enemy come against us, and we will say to them, “I can do all things, through Christ Jesus our Lord, which strengthens me.” For of “two sparrows which are sold for a farthing,” as the Scripture says, “not one of them falls on the ground without our Father in heaven.” And so completely does the Divine Providence embrace all things, that not even the hairs of our head fail to be numbered by Him.
Source: Against Celsus (New Advent)