Short answers, pulled from the story.
Christian music is a genre written to express personal or communal belief about Christian life and faith. Its main themes include praise, worship, penitence, and lament, and its forms range from ancient chant to contemporary hip-hop and electronic dance music.
Pope Gregory I, who reigned from 590 to 604 CE, was the first person acknowledged to have ordered chant music in the church, giving rise to the term Gregorian chant. He favored a simple, monophonic sound, believing that musical complexity tended to produce cacophony.
Martin Luther wrote hymns including "Ein feste Burg ist unser Gott" and "Gelobet seist du, Jesu Christ." He and his followers used chorales to teach tenets of the faith to worshipers. The first Protestant hymnal was published in Bohemia in 1532 by the Unitas Fratrum.
The Christian music industry grew out of the Jesus movement beginning in the 1970s and developed into a near-billion-dollar enterprise. By the 1990s, the genre had eclipsed classical, jazz, and new-age music in sales.
The music of Jehovah's Witnesses is translated into upwards of 500 languages, placing it among the most translated music in the world. Their current hymnal is called Sing Out Joyfully to Jehovah, and recordings are made in as many languages as possible through a global network of studios.
The Ichthus Music Festival, which started in 1970 in the United States, was among the earliest; today festivals can draw upwards of 100,000 people worldwide. New Zealand's Parachute Music Festival, the largest in the Southern Hemisphere, began in 1989 and is held at Mystery Creek Events Centre outside Hamilton. England's Big Church Day Out Festival began in 2009 and draws approximately 20,000 people annually.