The Polyeleos (Greek: Πολυέλεος, lit. "much oil" or, by connotation, "much mercy") is a festive portion of the Matins or All-Night Vigil service as observed on higher-ranking feast days in the Eastern Orthodox and Byzantine Rite Catholic Churches. The name came to be applied to this period of the festal service because at this time all of the oil lamps in the church are lit, using much oil. The Greek word for olive oil is very similar to the Greek word for mercy; hence, the natural correlation of the two ideas. The Polyeleos is considered to be the high point of the service, and contains the reading of the Matins Gospel. Because of its liturgical importance, beautiful settings for the Polyeleos have been composed by Sergei Rachmaninoff and others.