Spock's dying had to be one of the most unexpected and traumatic moments in all of the Star Trek canon. However, it was also one of the most important moments, as it led to some much-needed character growth in Captain Kirk as he lost his closest friend because of his shortsightedness.
Given how needed Spock's death was, one would think that its reversal after public outrage was a shallow decision; however, the way the franchise handled the reversal of Spock's death was also a stroke of pure genius, as it retained Kirk's character arc and even managed to add an entirely new level of depth to Spock's character.
Reversing Spock's death in Star Trek was a masterstroke for the franchise
Star Trek II: The Wrath of Khan was clear from the very beginning that it wanted to stand apart from its predecessors and the original series. It did so by being much more grounded in the story and much more mature than the others, which were known for their quirky space missions and morality stories.

The Wrath of Khan managed to do this by finally forcing Captain Kirk to grow up and face up to the consequences of his actions. Captain Kirk spends most of the film feeling vulnerable about growing up; however, when Spock ends up sacrificing his life for the greater good, Kirk is faced with the loss of his closest friend, Spock.
However, the audience did not have a passive response to this change, as they were reeling over Spock's death. Extreme outrage from the fans and witnessing their heartbreak over Spock's death in Star Trek made the creators reconsider their decision and bring Spock back to life. This could've meant that they were reversing all the character growth that Captain Kirk goes through as a result of his closest friend's death.

But Star Trek managed to figure out a way of bringing Spock back that would keep Captain Kirk's character growth and bring in some much-needed depth into the Vulcan's logic-based psyche. Spock was brought back through the science of the Genesis planet, which meant that he was regenerated from his birth.
This also meant that he was, in a way, a completely new Spock who had to be reeducated and even seemed to struggle with the questions when he was asked how he was feeling. However, with time, the Spock who returns is much different from the Vulcan Spock we were used to seeing. He is much less unyielding than before when it comes to his logic. Showing character growth in Spock through his regeneration was a masterstroke.
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