JST WAS FAR MORE THAN A MENTAL EXERCISE
The attitude with which Joseph Smith approached his assignment of the Bible translation is evident in statements by the Prophet. For example, in a letter to W.W. Phelps, Joseph explained: “We have finished the translation of the New Testament great and glorious things are revealed, we are making rapid strides in the old book and in the strength of God was can so all things according to his will.” [sic]  That Joseph and his scribe recognized that the work of the Bible translation was far more than a mental exercise is apparent in a simple entry at the top of page 1 of the manuscript of Matthew: “A translation of the New Testament translated by the power of God.”  In a revelation to Sidney Rigdon, the principal scribe for the translation, Jesus Christ gives to us His own perceptions of the nature and scope of the JST: “And a commandment I give unto thee—that thou shalt write for him: and the scriptures shall be given, even as they are in mine own bosom, to the salvation of mine own elect” (D&C 35:20; emphasis added).
SOMEONE ELSE TRIES TO TRANSLATE THE JST
After the foregoing was received [D&C 67], William E. M’Lellin, as the wisest man, in his own estimation, having more learning than sense, endeavored to write a commandment like unto one of the least of the Lord’s, but failed; it was an awful responsibility to write in the name of the Lord. The Elders and all present that witnessed this vain attempt of a man to imitate the language of Jesus Christ, renewed their faith in the fulness of the gospel, and in the truth of the commandments and revelations which the Lord had given to the Church through my instrumentality; and the Elders signifies a willingness to bear testimony of their truth to all the world. History of the Church, 1:226