as Conservative Anabaptist groups—such as the Dunkard Brethren Church and Conservative Mennonites), some Presbyterian churches devoted to the regulative principle of worship, Old Regular Baptists, Primitive Baptists, Plymouth Brethren, Churches of Christ, Church of God (Guthrie, Oklahoma), the Reformed Free Methodists, Doukhobors, and the Byzantine Rite of Eastern Christianity. Certain high church services and other musical events in liturgical churches (such as the Roman Catholic Mass and the Lutheran Divine Service) may be a cappella, a practice remaining from apostolic times. Many Mennonites also conduct some or all of their services without instruments. Sacred Harp, a type of folk music, is an a cappella style of religious singing with shape notes, usually sung at singing conventions. Opponents of musical instruments in the Christian worship believe that such opposition is supported by the Christian scriptures and Church history. The scriptures typically referenced are Matthew 26:30; Acts 16:25; Romans 15:9; 1 Corinthians 14:15; Ephesians 5:19; Colossians 3:16; Hebrews 2:12, 13:15 and James 5:13, which show examples and exhortations for Christians to sing. There is no reference to instrumental music in early church worship in the New Testament, or in the worship of churches for the first six centuries. Several reasons have been posited throughout church history for the absence of instrumental music in church worship. Christians who believe in a cappella music today believe that in the Israelite worship assembly during Temple worship only the Priests of Levi sang, played, and offered animal sacrifices, whereas in the church era, all Christians are commanded to sing praises to God. They believe that if God wanted instrumental music in New Testament worship, He would have commanded not just singing, but singing and playing like he did in the Hebrew scriptures. Instruments have divided Christendom since their introduction into worship. They were considered a Roman Catholic innovation, not widely practiced until the 18th century, and were opposed vigorously in worship by a number of Protestant Reformers, including Martin Luther (1483–1546), Ulrich Zwingli, John Calvin (1509–1564) and John Wesley (1703–1791). Alexander Campbell referred to the use of an instrument in worship as "a cow bell in a concert". In Sir Walter Scott's The Heart of Midlothian, the heroine, Jeanie Deans, a Scottish Presbyterian, writes to her father about the church situation she has found in England (bold added): The folk here are civil, and, like the barbarians unto the holy apostle, have shown me much kindness;