Why did Christianity threaten the Roman government?

Christians did not set out to threaten the Roman government, but the Roman leaders were worried that Christianity threatened the security of the state. This led to sporadic persecution of the Christians, undertaken in an attempt to force them to return to the traditional religion.

The Romans believed that they were favoured by all the gods because they were so devoted to them. In line with this attitude, they encouraged all conquered peoples to continue to worship their traditional gods. In special cases, they even took the statues and sacred objects of some gods back to Rome, and they worshipped them there, as well.

Christianity undermined that fundamental self-understanding of their military and political success. Christianity taught that all people should abandon the old gods, and worship God alone. Therefore, the Romans had a continuing concern that Christianity threatened the state because it did not respect the traditional gods of the Romans or of the conquered peoples.

While the Jews also taught that there is only one God, their religion was officially permitted from the time they were first conquered. This permission was not lost, even after the Jewish temple was destroyed in AD 70, since Judaism was the ancient religion of a conquered people. This fitted nicely into the Roman idea of their special kind of piety, namely to respect the traditional religions of conquered peoples.