and Methodist liturgy, examples are Te Deum and Benedicite. Prudentius, a Spanish poet of the late 4th century was one of the most prolific hymn writers of the time. Early Celtic hymns, associated with Saint Patrick and Saint Columba, including the still extant, Saint Patrick's Breastplate, can be traced to the 6th and 7th centuries. Catholic hymnody in the Western church introduced four-part vocal harmony as the norm, adopting major and minor keys, and came to be led by organ and choir. The Protestant Reformation resulted in two conflicting attitudes to hymns. One approach, the regulative principle of worship, favored by many Zwinglians, Calvinists among others, considered anything that was not directly authorized by the Bible to be a novel and Catholic introduction to worship, which was to be rejected. All hymns that were not direct quotations from the Bible fell into this category. Such hymns were banned, along with any form of instrumental musical accompaniment, and organs were ripped out of churches. Instead of hymns, Biblical psalms were chanted, most often without accompaniment. This was known as exclusive psalmody. Examples of this may still be found in various places, including the "free churches" of western Scotland. The other Reformation approach, favored by Martin Luther, produced a burst of hymn writing and congregational singing. Luther and his followers often used their hymns, or chorales, to teach tenets of the faith to worshipers. The earlier English writers tended to paraphrase biblical text, particularly Psalms; Isaac Watts followed this tradition, but is also credited as having written the first English hymn which was not a direct paraphrase of Scripture. Later writers took even more freedom, some even including allegory and metaphor in their texts. Charles Wesley's hymns spread Methodist theology, not only within Methodism, but in most Protestant churches. He developed a new focus: expressing one's personal feelings in the relationship with God as well as the simple worship seen in older hymns. The Methodist Revival of the 18th century created an explosion of hymn writing in Welsh, which continued into the first half of the 19th century. African-Americans developed a rich hymnody out of the spirituals sung during times of slavery. During the Second Great Awakening in the United States, this led to the emergence of a new popular style. Fanny Crosby, Ira D. Sankey, and others produced testimonial music for evangelistic crusades. These are often designated "gospel songs" as distinct