An ancient Hebraic hymn that has, in various instances, a doxological, penitential, didactic, or messianic content. In many respects, psalms served as models for the composition of new Christian hymns, and also came to be incorporated as important elements into all forms of the Christian liturgy. Following Hebraic antecedents, the Christians developed various styles of performing psalms: psalmodic chanting by one or several singers, antiphonal singing by two singers or groups, and responsorially -- when a single singer chanted the verses of a
psalm and the congregation responded with a refrain. Some psalms (or select verses) constitute hymns of the Ordinary in Orthodox services; others are hymns of the Proper for specific feasts.