Please see The Carols We Love: The "Story Behind the Story of Twenty-two Classic Christmas Carols, Daniel Partner, Barbour Publishing, Uhrichsville, OH, 2002.
"We Three Kings" is the most memorable work of John Henry Hopkins Jr. who was was a church man and music teacher for the most part. He did publish a book of carols, another book of poems, and the biography of his father, a prominent Episcopalian priest. "We Three Kings" is prominent for its message. The story of the Three Kings is found in Matthew chapter 2. The number of kings is not given, but they brought gold frankincense and myrrh. There is a verse describing each of the gifts, and then a conclusionary statement: "King and God and sacrifice. The gold represented Jesus as king, the frankincense as God (it was used in the temple) and the myrrh told of his final sacrifice. Myrrh was used in embalming.