19 This great modesty, this fixed determination to obey, was so well known that it could not be obscured by the calumny and malice of enemies. On this account, those who were going to plead in public before the emperors for any persons bearing the Christian name proved by this argument especially that it was unjust to enact laws against the Christians because they were in the sight of all men exemplary in their bearing according to the laws. Athenagoras thus confidently addresses Marcus Aurelius Antoninus and Lucius Aurelius Commodus, his son: "You allow us, who commit no evil, yea, who demean ourselves the most piously and justly of all toward God and likewise toward your government, to be driven about, plundered and exiled."(24) In like manner, Tertullian openly praises the Christians because they were the best and surest friends of all to the Empire: "The Christian is the enemy of no one, much less of the emperor, whom he knows to be appointed by God, and whom he must, therefore, of necessity love, reverence and honor, and wish to be preserved together with the whole Roman Empire."(25) Nor did he hesitate to affirm that, within the limits of the Empire, the number of enemies was wont to diminish just in proportion as the number of Christians increased.(26) There is also a remarkable testimony to the same point in the Epistle to Diognetus, which confirms the statement that the Christians at that period were not only in the habit of obeying the laws, but in every office they of their own accord did more, and more perfectly, than they were required to do by the laws. "Christians observe these things which have obtained the sanction of the law, and in the character of their lives they even go beyond the law."(27)
Source: Diuturnum (Vatican.va)