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Moses was transfigured in order that he could see God and endure his presence.
An example of this happening is seen in the Pearl of Great Price where it is recorded that Moses "saw God face to face, and he talked with Him, and the glory of God was upon Moses; therefore Moses could endure His presence" (Moses 1:2). Moses confirmed that it was because he was transfigured by the glory of God that he did not die when he saw the Lord's face while in mortality (see Moses 1:11). The Lord verified to Moses in yet another text that sinful mortals cannot see His face and live (see JST Exodus 33:20).
Joseph Smith recorded that he was "filled with the Spirit of God" during the First Vision
This brings us to the case of Joseph Smith in 1820. In the earliest known account of this heavenly manifestation (written in 1832 - the same year as D&C 84) the Prophet made note of the fact that when the experience began a pillar of fire rested down upon him and he was "filled with the Spirit of God." Once the heavens were opened the Savior appeared and said, "Joseph, my son, thy sins are forgiven thee." The Redeemer tied these elements together in a Book of Mormon passage where He informed a multitude of His disciples that certain persons would be "visited with fire and with the Holy Ghost, and shall receive a remission of their sins (3 Nephi 12:2). Since the Prophet's experience followed the same pattern, it is reasonable to believe that this is what happened to him in the Sacred Grove.
There are two further pieces of evidence pointing to the conclusion that Joseph Smith was transfigured during the First Vision event. First, there is Orson Pratt's 1840 recounting of the incident wherein he relates that the pillar of fire or light "continued descending slowly, until it rested upon the earth, and [Joseph Smith] was enveloped in the midst of it. When it first came upon him, it produced a peculiar sensation throughout his whole system." [2] Joseph noticed that there was some sort of change wrought upon his body and it was of an extraordinary nature—something he was apparently not accustomed to. Second, we find a parallel between what happened to Moses after his transfiguration and that which happened to young Joseph after his theophany ended. In Moses chapter 1 we read:
9 "And the presence of God withdrew from Moses, that His glory was not upon Moses; and Moses was left unto himself. And as he was left unto himself, he fell unto the earth. [10] And it came to pass that it was for the space of many hours before Moses did again receive his natural strength like unto man."(Moses 1:9-10)
In the Charles Walker account of the First Vision, it is indicated that Jesus touched Joseph's eyes in order for him to be able to see him
Diary of Charles Lowell Walker, as told by John Alger:
2nd Feb Thurs [1893] Cold and chilly. Attended Fast Meeting.... Br John Alger said while speaking of the Prophet Joseph, that when he, John, was a small boy he heard the Prophet Joseph relate his vision of seeing The Father and the Son, That God touched his eyes with his finger and said “Jospeh this is my beloved Son hear him.” As soon as the Lord had touched his eyes with his finger he immediately saw the Savior. After meeting, a few of us questioned him about the matter and he told us at the bottom of the meeting house steps that he was in the House of Father Smith in Kirtland when Joseph made this declaration, and that Joseph while speaking of it put his finger to his right eye, suiting the action with the words so as to illustrate and at the same time impress the occurence on the minds of those unto whom He was speaking. We enjoyed the conversation very much, as it was something that we had never seen in church history or heard of before.[3]
In three of the Prophet's retellings of the First Vision story he mentions that he too lost his strength and fell to the earth
1838 Main Text and Note B
"When I came to myself again I found myself lying on my back looking up into heaven; When the light had departed I had no strength, but soon recover[ed] in some degree."
1843 David N. White Interview
"when I came to myself, I was sprawling on my back and it was some time before my strength returned."
1844 Alexander Neibaur Diary
"I endeavored to arise but felt uncom[monly] feeble."
Some early Christian authors saw things in the same way as Joseph
For example, in an early Christian document called the Clementine Homilies the apostle Peter is portrayed as agreeing:
For I maintain that the eyes of mortals cannot see the incorporeal form of the Father or Son, because it is illumined by exceeding great light. . . . For he who sees God cannot live. For the excess of light dissolves the flesh of him who sees; unless by the secret power of God the flesh be changed into the nature of light, so that it can see light. [4]
Notes
Stephen E. Robinson and H. Dean Garrett, A Commentary on the Doctrine and Covenants: Volume Three (Salt Lake City: Deseret Book, 2004), 32-33.
Orson Pratt, An Interesting Account of Several Remarkable Visions (Edinburgh, Scotland: Ballantyne and Hughes, 1840), 5. off-site off-site Full title GL direct link
Karl Larson and Katharine Miles Larson, eds., Diary of Charles Lowell Walker (Logan, UT: Utah State University Press, 1980), 2:755–56 [recorded 2 February 1893]
Apostle Peter (claimed), "Clementine Homilies," in 17:16 Ante-Nicene Fathers, edited by Philip Schaff (Christian Literature Publishing Co., 1886)8:322–323.
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