How did Saints Cyril and Methodius help develop Old Church Slavonic?

Saints Cyril and Methodius were instrumental in the development of Old Church Slavonic as the first Slavic literary language. In 863, at the request of Prince Rostislav of Great Moravia, the brothers began a mission to establish a national church with its own language and writing system to counteract the influence of the Western Church.12

To facilitate this, they performed the following key actions:

• Creation of a Writing System: St. Cyril is credited with inventing the Glagolitic alphabet, a script specifically designed to represent the sounds of the Slavic languages using Greek-based characters.134
• Translation of Religious Texts: They translated the Bible and liturgical texts into the language now known as Old Church Slavonic, which was based primarily on the South Slavic dialects of their native Thessalonica.13
• Establishment of Slavic Liturgy: The brothers successfully advocated for the use of this vernacular language in church services, obtaining formal authorization from the papacy to conduct the liturgy in Slavonic.1

Their work provided the foundation for a shared literary tradition that spread across Slavic regions, profoundly influencing the development of Cyrillic and modern Slavic literary languages.134