Mormon, in abridging the library of records into this smaller record known as the Book of Mormon, indicated that “it is expedient that all people should know the things written” in the Book of Ether (see Mosiah 28:19). The events in the beginning of the Book of Ether happened at the time of the building of the tower of Babel and the confounding of man’s language. This was many centuries before Lehi’s vision that begins the Book of Mormon. I've often wondered why it is that the Book of Mormon doesn't begin with the Book of Ether. It’s chronologically presented otherwise. Why wait until the end of the book to tell us about what happened at the beginning of it? Chapter 4 contains an answer to this question. In verse 1 we learn that the Lord told the brother of Jared to write what he had learned in the amazing conversation of the previous chapter, but that these things were not to be shared with people until after Jesus had died on the cross. So it was about 400 years after that terrible and blessed event that, Moroni, being alone, added the Book of Ether to the sacred record that he was keeping. We have the portion of it that is available to us thanks to Moroni.