Warning: spoilers ahead for the fall premiere of Supernatural Season 15, called "Last Holiday."
Supernatural is back on The CW after the long and unplanned hiatus in the final season, and the back half of Season 15 got off to a festive start with "Last Holiday." There was a sinister side to the wood nymph known as Mrs. Butters, however, and it was only after Sam and Dean managed to stop her from killing Jack that she dropped what might turn out to be a key reveal for the battle against God. At long last, Supernatural is bringing in that mysterious Men of Letters bunker telescope.
Mrs. Butters used her magic to temporarily raise the power of the Men of Letters bunker out of standby mode, and that included powering up the telescope that has been in the background of the bunker for years now without anybody trying to use it. According to the wood nymph, the telescope isn't actually a telescope at all, and I'm inclined to think that it's going to be important.
In the closing minutes of "Last Holiday," Mrs. Butters revealed that it's actually an "interdimensional geoscope," then said "that's not good" when Dean stated that he didn't see anything when he looked in it earlier. Jack changed the subject before the Winchesters could get any more information out of Mrs. Butters, but surely Supernatural wouldn't wait until the last seven episodes of the final season to bring the interdimensional geoscope in if it's not going to be important, right?
On the one hand, it is entirely possible that the interdimensional geoscope was a device designed to see between universes in the Supernatural multiverse, and Dean not seeing anything through it might simply have been subtle confirmation that God finished extinguishing all the other galaxies. What leads me to believe that the geoscope still has a part to play was the lingering shot of the device powering down after Mrs. Butters left. If it wasn't important, why focus on it again, especially when it has been in the background for so long? Chekhov's telescope!
An interdimensional geoscope is definitely not something that Dean has been transporting in the back of Baby for the past decade and a half, and it sounds to me like it has cosmic connections. If so, it could come in handy in the battle against God, which of course also now includes a battle against Amara since one dying and the other living would throw everything out of balance. I'm not entirely sure what the geoscope does, so I can't speculate too much about what role it could play, but something kept in the Men of Letters bunker would ideally work in Team Free Will 2.0's favor.
Even if the interdimensional geoscope isn't too useful beyond confirming damage already done by God, that makes it an asset to the Winchesters. Any small advantage could make all the difference when it comes to killing God, especially when their hopes ultimately rest on Jack succeeding, and there's an awful lot of pressure on the shoulders of a guy who just got his soul back. If Castiel is dragged to The Empty before the finale, they might be short on trustworthy allies as well.