Final answer:
Christians were considered atheists in Nero's time because they refused to participate in local religious festivals and imperial cults, seen as a rejection of Roman gods and a challenge to the social order. Their unique worship practices and monotheistic beliefs set them apart, leading to periodic persecution. The conversion of the empire to Christianity eventually halted such conflicts.
Step-by-step explanation:
During Nero's time, Christians were considered atheists because they did not celebrate the festivals of the local gods. Christians were viewed by Roman authorities as challengers to worldly authority and as disruptive to societal norms due to their refusal to participate in traditional rites such as animal sacrifice.
The earliest record of violent persecution against Christians dates back to 64 CE, under Emperor Nero's reign, who blamed the Christian community for the Great Fire of Rome. Over time, this led to sporadic periods of official persecution, with emperors like Diocletian intensifying these efforts, largely due to Christians' avoidance of the imperial cult, which was seen as treasonous.
Christian methods of worship, which included prayers, communal feasting, and practices like baptism, starkly contrasted with pagan ceremonies and further exacerbated tensions. These divergent practices, coupled with Christianity's evangelistic drive to convert others and its inherent lack of tolerance for polytheism, posed a threat to the hierarchical and religious structures of Roman society. By the late fourth century, however, the state religion of the empire shifted to Christianity under Emperor Theodosius I, which marked a significant turn in Rome's religious landscape.