The phrase "or out of the waters of baptism" (1 Nephi 20:1) first appeared in the 1840 and 1842 editions of the Book of Mormon. It did not appear again until the 1920 edition, and it has been in all editions since that time. According to McConkie and Millet, it appears to be a prophetic commentary by Joseph Smith to explain the meaning of the phrase "out of the waters of Judah." Such editorial comments by modern rules of [style] would be identified by the use of brackets. If this phrase were a restoration of the original text, as found in the more pure version on the brass plates from which it comes, it would have appeared in the 1830 edition of the Book of Mormon, and we would also expect to find it in the Joseph Smith Translation of Isaiah 48:1, but we do not.
Through the use of this phrase, Joseph Smith is calling our attention to the fact that the ordinance of baptism was as common to the people of the Old Testament as it was to the people of the Book of Mormon. [Joseph Fielding McConkie and Robert L. Millet, Doctrinal Commentary on the Book of Mormon, Vol. 1, pp. 151-152] [For information on the practice of baptism in O.T. times, see the commentary on 2 Nephi 31:6]