A “truth” was now defined and enforced by law
Charles Freeman on a crucial moment in history (from The Closing of the Western Mind):
In January 381 Theodosius issued an imperial decree declaring the doctrine of the Trinity orthodox and expelling Homoeans and Arians from their churches…
This council, together with the imperial edicts which accompanied it, was the moment when the Nicene formula became part of the official state religion (if only for the moment in the Eastern empire). All those Christians who differed from it – Homoeans, Homoiousians, Arians and a host of other minor groups – were declared to be heretics facing not only the vengeance of God but also that of the state. The decision of Constantine to privilege one Christian community over another was consolidated in that a “truth” was now defined and enforced by law, with those declared heretical to be punished on earth as well as by God. It was unclear on what basis this “truth” rested, certainly not one of exclusively rational argument, so it either had to be presented as “the revelation of God,” as it was by Thomas Aquinas, or accepted that “truth” was as defined by the emperor. [pp 193, 194]
Not what you would call a science-friendly world, then.