Letter to Svatopluk I, King of Slavs

In this letter Pope Stephen V informs Svatopluk I, the king of the Slavs (Moravians), along with all the nobles and people of the nation, that God chose the institution of the papacy to be be his protector in all matters. The pope embraces him as a spiritual son, and welcomes into the fold of the Christian faith. At his request, he explains to him the Roman doctrine of the Trinity, which Svatopluk, appears to be unfamiliar with. He is surprised that Methodius would teach a potential Trinitarian error, and forbids celebrating divine services in the Slavic language, but recommends the interpretations of the Gospel and the apostle in the same language. Pope Stephen also orders disobedient clergy to be expelled from the church and expelled from the country altogether via royal decree.