Mormon Beliefs: Open Scripture
Mormonism is unique among Christian denominations in its acceptance of scripture other than the Bible. Revelation to modern prophets, and the translation of the Book of Mormon, have revealed that Adam kept a Book of Remembrance, as have many prophets since; that many scriptures already written have not yet come to light–such as the writings of Joseph (who was sold into Egypt) and John the Baptist; and that additions to existing scriptures can be made by current prophets for edification of believers now and in the future. The following is a quote from an Ensign magazine article which appeared in 1989:
Unlike traditional Christianity, which remains a religion of the book (the Bible), the restored gospel from its beginning has been a religion of books. Joseph Smith’s contribution to the concept of scripture is important and unique.
The translation of the Book of Mormon assured from the birth of the Church an openness to scriptural texts outside the Bible. Its appearance established that God still speaks through prophets and that the Bible is not an exhaustive collection of scripture. The Book of Mormon expressly cautions readers: “Because that ye have a Bible ye need not suppose that it contains all my words; neither need ye suppose that I have not caused more to be written.” (2 Nephi 29:10.)
It goes even further, pronouncing a woe upon those who say, “We need no more of the word of God, for we have enough.” (2 Nephi 28:29.)
From the writings of Nephi, Joseph Smith learned that the Book of Mormon would be only one of many books to come forth in the last days. (See 1 Nephi 13:39; 2 Nephi 27:11.) The pages of the Book of Mormon also contain interpretations, additions, and corrections to chapters from Isaiah, as well as quotations from heretofore unknown prophets of ancient Israel (Zenos and Zenock, for example), together with a precious account of the resurrected Savior’s personal ministry among inhabitants of ancient America.
From the Book of Mormon, Joseph had his concept of scripture greatly expanded. The translation of the Nephite scripture gave concrete evidence that the Lord had spoken to “all men, both in the east and in the west, and in the north, and in the south,” and that they had written God’s words by which he “will judge the world.” (2 Nephi 29:11.) New scripture promotes faith in other sacred texts. Mormon 7:9 adds that the Nephite records were “written for the intent that ye may believe [the Bible].” [Mormon 7:9]
Between the time the Book of Mormon was published and the Kirtland Temple was dedicated, Joseph Smith learned that God had given power and knowledge to man in a series of dispensations. (See Doctrine and Covenants 27:12–13; Doctrine and Covenants 110:12, 16.) Beginning with Adam, each dispensation had been given holy scripture “according to their language, unto their understanding.” (2 Nephi 31:3.) Restoring lost knowledge from those earlier dispensations was a part of the restoration of all things, as the receipt of the Book of Moses in 1830 richly illustrated.
In none of these things, however, did Joseph Smith think any less of the Bible as far as it was translated correctly. (See Articles of Faith 1:8.) Indeed, as early as 1830, Joseph devoted great energy to improving our understanding of the King James Bible. He considered this work a “branch of [his] calling,” and he spent many hours studying and restoring proper meaning to many passages. In all, Joseph Smith altered about 3,400 verses in the Bible—about 10 percent of the total. Because this task was not completed—and for other reasons—we use the King James Version. The LDS Church’s printing of the KJV does not alter the scripture, but does include footnotes through which the reader can view the Joseph Smith translation of certain verses, and the full Joseph Smith translation of parts of Matthew, included as an appendix.
In addition to restoring ancient principles, Joseph Smith added new revelations to the body of scripture: the volume of sacred writ was not to be closed. Many of these revelations were communicated during regular conferences, then printed in official reports. Significantly, these revelations stand as scripture itself: “What I the Lord have spoken, I have spoken, … my word shall not pass away, but shall all be fulfilled, whether by mine own voice or by the voice of my servants, it is the same.” (Doctrine and Covenants 1:38.)
Thus, by experience and revelation, Joseph learned and taught (1) that scripture is nothing more or less than the word of the Lord, (2) that the book of God’s word is not closed, (3) that God speaks to all dispensations, (4) that scripture must be correctly understood through the spirit of truth, and (5) that the words of the Lord’s servants when moved upon by the Holy Ghost are scripture, too. (See 2 Peter 1:20–21; Doctrine and Covenants 68:4.)
These doctrines came into Joseph Smith’s world as radical ideas. Joseph’s Christian contemporaries accepted as scripture only the books of the Bible. They considered that volume to be a single, complete, and absolute source to be understood quite literally. Thus, the laws of the Massachusetts Bay Colony described the Old and New Testaments as “containing in them the infallible and whole Will of God, which he purposed to make known to Mankinde,” the denial of which was punishable by fines, whippings, banishment, or death.
To people of such persuasion, the ideas of continuous revelation, additional scripture, dispensations, inspired versions, and gifts of prophecy evoked sharp reactions. For example, two months after the publication of the Book of Mormon, the Palmyra Reflector warned Oliver Cowdery that he might be sent as a convict to the Simsbury Mines if he dared to proclaim its message in “the principal cities of the Union.”
The rejection of new revelation in the 1830s was similar to the rejection of new revelation by the Jews at the time of Christ. Many Jews whom Jesus encountered insisted that the receipt of new scripture was impossible, that the law was complete (as they interpreted Leviticus 27:34 to say), and that prophecy had ceased after the second century b.c.
For the early Christians, however, the floodgates of revelation had just opened again. The Epistle to the Hebrews begins with a bold declaration of new revelation: “God, who at sundry times and in divers manners spake in times past unto the fathers by the prophets, hath in these last days spoken unto us by his Son.” (Hebrews 1:1–2.)
John declares likewise: “The Revelation of Jesus Christ, which God gave unto him, to shew unto his servants things which must shortly come to pass.” (Revelation 1:1.)
To these early followers of Jesus, the scriptures were not a closed set of writings. To the Apostle Paul, for example, all writings inspired by God were good for doctrine and the promotion of righteousness. (See 2 Timothy 3:16.)
In Paul’s day, there was no fixed collection of books, even among the Jews, that exclusively counted as scripture. Thus, Jude 1:14–15 quotes without reservation the nonbiblical book of Enoch as scripture. Indeed, not until the fourth century did the New Testament canon become fixed, and not until the Reformation in the sixteenth century did the church regard the Old Testament as Jerome did—that is, as the Hebrew canon.
Matthew, Paul, and Jesus himself led the way in showing, as Joseph Smith did, the need for expounding, searching, and interpreting the scriptures in light of current conditions and true perceptions (see Matthew 22:23–33; Matthew 24:27; John 5:39), and in issuing new commandments (see John 13:34; 1 Corinthians 6:7–8). They recognized the impossibility of restricting their spiritual knowledge to a finite number of pages. (See John 21:25.) Thus we see an open and complex idea of scripture in the early Christian movement that is comparable to the expanding view of scripture understood by Joseph Smith. 
See Mormon Scriptures: The Bible; Mormon Scriptures: The Book of Mormon; Mormon Scriptures: The Doctrine and Covenants; Mormon Scriptures: The Pearl of Great Price; Is the United States Mentioned in the Bible?