Star Trek: Discovery has revisited a Star Trek: The Next Generation two-parter, and cemented Spock's amazing legacy in the process. As "Unification III" begins, the crew of the Discovery are now more fully acclimated to the 32nd century after their time jump, and Burnham and friends seek to find out all they can about the Burn, the cataclysmic event that happened a century earlier and wiped out the vast majority of dilithium - the fuel that powers warp engines - across the known galaxy.
During their investigation, Burnham learns that Vulcan could hold an important key to the mystery via a mothballed propulsion project called SB-19. She also learns that the planet is no longer called Vulcan, but is now Ni'Var, the home planet of both the Vulcans and the reunified Romulans. The Romulans - traditionally one of the Federation's most brutal and secretive enemies - reunified with their Vulcan cousins following the destruction of their home world, Romulus. And while forces as varied as Admiral Jean-Luc Picard and the Qowat Milat played role in reunification, the ultimate catalyst turned out to be Burnham's little brother, Spock.
In the classic Star Trek: The Next Generation two-parter "Unification," Spock is feared to have defected from Starfleet, as he wrapped up all of his affairs in the Federation and made his way to Romulus. Starfleet sends Captain Picard and Commander Data to ascertain Spock's true motives, which turned out to be very different than what was assumed. Spock became an integral part of the Romulan underground, which sought to embrace the teachings of Vulcan, rejecting the more cynical Romulan way of life.
Picard, a fellow supporter of reunification, thought Spock should have gone through official channels to initiate such a massive shift, but Spock didn't want to risk the lives of anyone else in his efforts. "Unification" ends with Spock still on Romulus, continuing his teachings and hoping for a day when the two races would finally come back together. "Unification III" confirms that his dream came to pass, and Burnham learns of Spock's crucial role in reunification in a touching moment where she looks up what became of her little brother, complete with a clip of Leonard Nimoy as Spock from "Unification."
Star Trek: Discovery famously began as a prequel, and Spock (played by Ethan Peck) was a major part of the show's second season. The time jump to the 32nd century - as well as the Spock-starring upcoming series Star Trek: Strange New Worlds - means we've likely seen and heard the last of the legendary Vulcan on Discovery. Affirming his legacy as one of the most important Vulcans who ever lived is a great way to say goodbye to him.