When Christianity was in its infancy, the Emperor of Rome was considered a god. Around 45 BC the Jewish army helped Julius Caesar fight his wars, and so, the Jewish worship of Yahweh was tolerated. However, the Jews insisted that these Christians were not Jews and weren't excused from worshipping Caesar, as god.
The Christians acknowledged Caesar's authority to govern but would not worship him. Remember Matt 22: 20-21, They would pray for him, honor him, obey him, but he is only a man who God appointed to rule.
Art from Catacombs
Baptizing
