However, if we must refer briefly to the difference between the constitution which was given to the Jews of old by Moses, and that which the Christians, under the direction of Christ's teaching, wish now to establish, we would observe that it must be impossible for the legislation of Moses, taken literally, to harmonize with the calling of the Gentiles, and with their subjection to the Roman government; and on the other hand, it would be impossible for the Jews to preserve their civil economy unchanged, supposing that they should embrace the Gospel.
For Christians could not slay their enemies, or condemn to be burned or stoned, as Moses commands, those who had broken the law, and were therefore condemned as deserving of these punishments; since the Jews themselves, however desirous of carrying out their law, are not able to inflict these punishments. But in the case of the ancient Jews, who had a land and a form of government of their own, to take from them the right of making war upon their enemies, of fighting for their country, of putting to death or otherwise punishing adulterers, murderers, or others who were guilty of similar crimes, would be to subject them to sudden and utter destruction whenever the enemy fell upon them; for their very laws would in that case restrain them, and prevent them from resisting the enemy.
And that same providence which of old gave the law, and has now given the Gospel of Jesus Christ, not wishing the Jewish state to continue longer, has destroyed their city and their temple: it has abolished the worship which was offered to God in that temple by the sacrifice of victims, and other ceremonies which He had prescribed. And as it has destroyed these things, not wishing that they should longer continue, in like manner it has extended day by day the Christian religion, so that it is now preached everywhere with boldness, and that in spite of the numerous obstacles which oppose the spread of Christ's teaching in the world.
But since it was the purpose of God that the nations should receive the benefits of Christ's teaching, all the devices of men against Christians have been brought to nought; for the more that kings, and rulers, and peoples have persecuted them everywhere, the more have they increased in number and grown in strength.
Source: Against Celsus (New Advent)