Why did Christianity seem threatening to Roman government?

Several Roman emperors considered Christianity a problem. This lead to a number of persecutions. Christianity was at times (not always ) seen as a threat because it converted previously pagan Romans and it refused to perform sacrifices.

Roman religion was seen as a fundamental part of the Roman state. This state was seen as requiring the blessing of Roman gods for its security and welfare. The Romans believed that natural disasters were the result of wrath of the gods. Therefore, the gods had to be appeased by performing sacrifices in their honour. Moreover, actions which would involve public matters or the wellbeing of the state or war had to be preceded by augury. This was the divination of the omens of the gods to see whether they approved or disapproved of the proposed action.

Because of this view, the Christian refusal to perform sacrifices was at times seen as a threat to the foundation of the state, a threat which was made worse by the conversion of Romans to Christianity. Some of these Romans were rich people and some were officials in the imperial bureaucracy and court. Thus, the threat could be seen as reaching the core of the state. The attitude of the Christians could also raise the question of whether they were loyal to the Romans state. One of the Christian persecutions (the Decian persecution) was aimed at testing their loyalty. They were required to perform sacrifices and if they did not, they were liable to execution. This was done to test their loyalty to the imperial state.