In a note to Ether 3:15 in the 1879 edition of the Book of Mormon, Orson Pratt offered the following explanation of the passage:
When
the Lord appeared unto Adam and the righteous, and unto Enoch and the people of
ancient Zion, it was probably by vision, and not by full view of his personage,
as was given to the brother of Jared. See Doc. and Cov. 107:54. (p.
577 note L)