The Joseph Smith Translation (JST) is the King James Version of the Bible with Joseph Smith’s revisions—mostly in the form of additions, though with some other kinds of changes. Smith supposedly produced these revisions under divine inspiration.

Some Mormons view the changes as restoring the Bible text to its original wording. Other Mormons view the changes as a kind of modern commentary that clarifies the meaning or significance of what the Bible said. Some Mormons use both kinds of explanations depending on the specific passage. However, neither of these explanations will work. There are many changes to the Bible in the JST that cannot be explained as restoring the original text or as clarifying its meaning. Here are some examples of such changes in the JST version of the Book of Hebrews:

• Psalm 95:11 is quoted three times in Hebrews. The JST adds nothing to the first quotation (Heb. 3:11), adds 22 words to the second quotation (4:3), and adds 5 words to the third quotation just two verses later (4:5). Apparently, Joseph Smith didn’t understand that Hebrews was quoting the same Old Testament text in all three verses.
• Joseph Smith didn’t change the wording of Hebrews 4:8, which in the KJV refers to Joshua as “Jesus” (because the names are the same in Greek), even though this would have genuinely helped to clarify the meaning of the verse.
• Joseph added the word not to Hebrews 6:1, making it say, “Therefore not leaving the principles of the doctrine of Christ,” because he didn’t understand that “leaving” could mean “moving on from” or “advancing beyond” rather than “abandoning.”
• Misunderstanding Hebrews 7:3 in the KJV to mean that Melchizedek literally had no father or mother and never was born or died, Joseph Smith changed the text to say that Melchizedek “was ordained a priest after the order of the Son of God.” But this change turns around backward what the passage says six other times (where Joseph did not change the text), namely, that Jesus was “a priest after the order of Melchizedek” (Heb. 5:6, 10; 6:20; 7:11, 17, 21). Hebrews 7:3 does not mean that Melchizedek literally had no parents, birth, or death. It means that the mysterious appearance of Melchizedek in the passage in Genesis without any mention of these things makes him a suitable type of the Messiah, who literally was eternal (though in the Incarnation he did have human parents, was born, and died). Joseph Smith didn’t understand this, so he rewrote the verse—but in so doing created a conflict between this verse and the surrounding context.

These and other examples show that Joseph Smith’s “translation” was not divinely inspired, however one explains the significance of the changes from the KJV.

For a detailed, scholarly study of this topic—with extensive use of the Greek text—see the PDF file here.