Roman emperors Arcadius and Honorius, the sons of Theodosius I, issue a new law requiring a separation of church and business: any priest engaged in business trade has to choose one and leave the other.
According to this Roman law:
"We command that all members of guilds...surrender the exemption of clerics, or else, if they serve the Most Holy God, must abstain from shrewd pursuits of profits...
For the services of religion and those of shrewdness are distinct." [CT 13.1.16]
So in the Roman empire there is no separation of church and state, but there does have to be a separation of church and business or church and commerce.
Because of the significant tax exemptions accorded to churches and clergy over the years, it's likely that they have developed great advantages over secular businesses which will have resulted in considerable resentment.
Now that Christianity is more established, the granting of tax exemptions to business conducted by churches and clergy may not be as necessary as it once was.