If like me you wonder who are the Moravians, they are a group of Protestants founded in Saxony by folks who emigranted from Moravia. They believed the bible to the only source of faith, and held to many views of the Hussites (who were followers of John Huss). The Moravians were one of the first Protestant Groups to send out missionaries.
David has a quick affinity with other languages and quickly learned the languages of the Native People. This allowed him to serve as an interpreter for the government, but his true gift was travelling amongst the Native Americans, establishing mission stations as he went.
It was rather frustrating for him as the Native Americans would be driven out of their land and the mission stations he started destroyed so he needed to keep moving and restarting. In fact a rather sad moment occurred in his life (according to Wiki)
He was the senior missionary of the United Brethren (as the Moravians sometimes referred to themselves) among the Indians. His relations with British authorities worsened during the American Revolutionary War and in 1781 he was arrested and held at Fort Detroit. While he was imprisoned, ninety-six of his Native converts in Gnadenhutten, Ohio were brutally murdered by Pennsylvania militiamen, an event known as the Gnadenhutten Massacre.
In 1798 he established the Goshen Mission and stayed there the next 10 years, translating hymns and books into the language of the Delaware Indians. He taught many hymns to the converts, and while he lay dying they gathered around him singing hymns. (source)