Nephi does not explain why he could not take his father’s dream at face value but found it necessary to experience the dream’s content for himself. He simply cites his desire to see and know those things for himself. This development marks a new stage in Nephi’s relationship with his father-prophet. While Nephi has recorded his father’s visions, he has never indicated having a personal revelation about them. Why now?
Nephi was born after Josiah’s reform. While I have argued that Lehi maintained many of the older beliefs, it is unclear how much of this previous tradition Nephi would have known directly. Lehi was familiar with the symbolism of the tree of life and its connection to the temple, but Nephi probably was not. This probability is strengthened by Nephi’s record of his own vision. It does not simply repeat and explain the symbols but expands and explicates their connection to the Messiah, constituting, in part, a whole new revelation. Lehi’s symbolic system may have led him easily to that understanding, but Nephi had to have a more explicit explanation to see the Savior in the symbol.