The Slavs rejoiced to hear the greatness of God extolled in their native tongue. The apostles [Cyril and Methodius] afterward translated the Psalter, the Oktoechos, and other books.
…[S]ome zealots began to condemn the Slavic books, contending that it was not right for any other nation to have its own alphabet apart from the Hebrews, the Greeks and the Latins, according to Pilate’s superscription, which he composed for the Lord’s Cross. When the Pope at Rome heard of this situation, he rebuked those who murmured against Slavic books, saying:
“Let the word of Scripture be fulfilled that ‘all nations shall praise God’ (Ps. 71:17), and likewise that ‘all nations shall declare the majesty of God according as the Holy Spirit shall grant them to speak’ (Acts 2:4). Whosoever condemns the Slavic writing shall be excluded from the Church until he mend his ways. For such men are not sheep but wolves; by their fruits ye shall know them and guard aginst them. Children of God, hearken unto His teachings, and depart not from the ecclesiastical rule which Methodius your teacher has appointed to you.” (The Russian Primary Chronicle, 25)