But again, that it is not the fear of external enemies which strengthens our union, is plain from the fact that this cause, by God's will, has already, for a considerable time, ceased to exist. And it is probable that the secure existence, so far as regards the world, enjoyed by believers at present, will come to an end, since those who calumniate Christianity in every way are again attributing the present frequency of rebellion to the multitude of believers, and to their not being persecuted by the authorities as in old times.
For we have learned from the Gospel neither to relax our efforts in days of peace, and to give ourselves up to repose, nor, when the world makes war upon us, to become cowards, and apostatize from the love of the God of all things which is in Jesus Christ. And we clearly manifest the illustrious nature of our origin, and do not (as Celsus imagines) conceal it, when we impress upon the minds of our first converts a contempt for idols, and images of all kinds, and, besides this, raise their thoughts from the worship of created things instead of God, and elevate them to the universal Creator; clearly showing Him to be the subject of prophecy, both from the predictions regarding Him— of which there are many— and from those traditions which have been carefully investigated by such as are able intelligently to understand the Gospels, and the declarations of the apostles.
Source: Against Celsus (New Advent)