As a general rule, those who study Christianity’s growth and expansion—missiologists—know that a given culture has truly embraced the faith when its people compose their own songs for worship. Similarly, hymns that remain popular centuries after their composition are often traced to times of reformation and revival. Two well-known Christmas carols in the English language are Joy to the World, written by Isaac Watts (1674-1748), and Hark the Herald Angels Sing, by Charles Wesley (1707-1788).