Excuse me for repeating, but I’ve always been interested in the scripture passages that describe the clestialized Earth as a giant Urim and Thummim with which to view “inferior kingdoms”, and the white stones that members of the Church of the Firstborn will receive that will be used to view superior kingdoms. If those devices can view across dimensions of space, it makes me imagine that they can also view across the dimension of time.

As to why separate devices are needed with separate functions, I would suppose that it is because the three degrees of inhabitants of the Celestial Kingdom have different levels of privilege. As only the highest degree will go on to exaltation, they are the only ones to get the individual devices that view the higher levels. The lesser two degrees, which have no increase or progression, only get to see where they have been, or what they have surpassed, the “inferior” kingdoms; the present mortal and fallen earth being an “inferior” kingdom to the future celestialized Earth.

For the lower two levels to see what they are missing out on in higher future worlds, where they will never go, would likely cause a degree of sadness.