There was an opportunity with the introduction of artifacts in Destiny 2 that could give the players a device that would represent their journey through the narrative of that season. Having an object the players would continually revisit and build upon meant that it should be changing with them as they progressed and would hopefully encapsulate the overarching narrative of that season. 
In Season of Dawn, we brought back Osiris, a character the players know as the hyper-intelligent, time-traveling scientist who helps us rescue St XIV from his death in the past. 
The Lantern is an invention of Osiris, a device used to hone in on the correct frequencies of time. Similar to using a tuning fork to find the right note, the user would cycle through the various runes between consonant and dissonant wavelengths until they were in tune with the correct frequency, unlocking the doorway into that dimension.