… A careful reading of this scripture, particularly when read together with Nephi’s explanation, would indicate that the term it ‘hath a familiar spirit’ means that this record (the Book of Mormon) would speak with a ‘familiar voice’ to those who already have the Bible. In other words, Nephi is evidently saying here that the doctrinal teachings of the Book of Mormon would seem familiar to people who had already read and accepted the Bible.
(Daniel H. Ludlow, A Companion to Your Study of the Book of Mormon, p. 146)