The law issued in 380 in the names of Theodosius, Gratian and Valentinian II is short. It commands that all the peoples under their rule shall practise the religion which the apostle Peter delivered to the Romans, as followed by the bishop Damasus of Rome and by Peter, bishop of Alexandria, namely belief in the single deity of Father, Son and Holy Spirit in equal majesty and holy Trinity. Those who follow it shall take the name of catholic Christians; the rest are judged demented and insane, shall bear the infamy of heretical teaching, and are to be punished by divine and by imperial vengeance.
Two features of the drafting are worth attention. The law does not state the doctrine at length; it identifies it by naming two living bishops whose communion is the test. And it takes the name catholic, which the church had used of itself for two centuries, and makes it a legal category with consequences attached.
The immediate context was the Arian dispute, which had run for two generations with imperial support shifting between parties. Theodosius ended the shifting by legislating. The council he called at Constantinople the following year confirmed the doctrinal settlement, and within a decade further laws prohibited sacrifice and closed temples of the older cults.