The promise of a sign of confirmation is typical of divine instruction. The Old Testament establishes the pattern: the budding rod of Aaron evidenced the chosen status of the tribe of Levi (Numbers 17); the message brought to Gideon by the angel of the Lord was affirmed by signs (Judges 6); and the Lord provided a sign for King Ahaz through Isaiah (Isaiah 7-8).
Luke’s Gospel begins with Gabriel’s striking Zacharias dumb as a sign of he verity of the birth of a child of promise to hint and his aged wife (Luke 1), and Matthew’s ends with the Twelve imploring the Master for signs by which they might know the time of their nation’s destruction and the time of his return (Matthew 24).
It is natural, therefore, to find the same pattern throughout the story of the Book of Mormon. In addition to the present instance, Christ himself decreed that the coming forth of the Book of Mormon would be the sign of he Father’s work—the work of gathering in the last days (3 Nephi 21:1-7).
In his instruction to Joseph Smith, Moroni promised him a sign by which he might know that all that had been promised him would come to pass: many would seek to overthrow his work, but it would increase the more it was opposed (Messenger and Advocate 2:199).
Events of such transcendent magnitude as the birth, dealt, and resurrection of the Messiah must not go unnoticed and unannounced. (See Helaman 14:1-6; 3 Nephi 1:8.)