Moses 1

Moses noted that after his conversation with Jehovah -

"But now mine own eyes have beheld God; but not my natural, but my spiritual eyes, for my natural eyes could not have beheld; for I should have withered and died in his presence; but his glory was upon me; and I beheld his face, for I was transfigured before him."  (Moses 1:11)

Also -

"For behold, I could not look upon God, except his glory should come upon me, and I were transfigured before him."  (Moses 1:14)

This would suggest to me that all ancient prophets that beheld Jehovah must have been transfigured.

Maybe when the Brother of Jared saw the hand of the Lord, he wasn't yet transfigure, thus the comment -

"...never have I showed myself unto man whom I have created, for never has man believed in me as thou hast."  (Ether 3:15)