I suggest that the physical object that Joseph had in his possession was not literally ancient gold plates, but plates of his own creation which talismanically represented the "gold plates" of his visions, aiding his mystical translation of those visions.
One of the major themes in Disney's Frozen II is the journey into the unknown, which is a common element of the mystical journey into communion with the Divine.
Physics tells us that all things are made up of massless light-speed particles that have become bound together giving rise to mass and spacetime. Is this the Incarnation?
Many people want to know the ultimate nature of the universe, the ultimate reality. Many seek it through science. But mysticism and contemplation may offer the Way that actually realizes that One, which is Love.
In a truly stunning paradox, extremes can flip around into their shadow opposites. They can also reveal a transcendent unity, or greater Whole.
As science seeks a unified theory of everything, of reality as a whole, we may need to focus more on contemplating the nature of consciousness and our own self to find the answer.
This song is almost like a "First Vision" in itself, full of mystical allusions and symbols, suddenly realizing the Light, the Love, the One.
Where does spacetime come from? Might our mind generate it as a kind of illusion in consciousness? How might we transcend this illusion in contemplation?
Do those who suddenly die realize heaven the same as those who die slowly? Will we remember our life, will our experiences be saved? What is the purpose of God incarnating?
The opening lullaby in Frozen II is replete with mystical symbolism of all kinds, which frames the rest of the film's story.