Isaiah worked in the
Matejče Monastery, near
Kumanovo (in modern
North Macedonia). He was a prolific author of
acolouthias (in
Old Church Slavonic послѣдованиѥ). Each
acolouthia was an anthology of liturgical chants and
psalm settings, both his own and others'. Isaiah was a very well-educated composer of both bilingual and purely
Greek hymns. His masterpiece,
Serbian Polyeleos, appears in two manuscripts, one version with a
Serbian recension of the text, the other with a Greek. The existence of Greek and Slavonic settings in his works shows that Serbian services were commonly bilingual. He was also the author of the bilingual
Trisagion. Many of his works are short syllabic hymns honouring the Serbian saints. Isaiah's melodies, some syllabic and others more melismatic, demonstrate his inventiveness and ability to introduce new and original elements, especially from the Serbian tradition, within the compositional framework of Byzantine chant, thus creating a new and distinctive style: the Serbo-Byzantine school. His works represent two-thirds of preserved Serbian Medieval music. He was also immensely popular after his death, with his compositions being copied until the late 18th century. His works are also included in the
Anthologion 928 from the
National Library of Greece,
Athens. ==Selected works==