Prior to the release of The Last Jedi, audiences wondered if we'd see Luke Skywalker wield a lightsaber and, if so, what color that saber would be. While we did technically see Luke wield a lightsaber, in a manner of speaking, those moments resulted in even more questions about the character. According to Rian Johnson, Luke opting to use a blue saber in his confrontation with Kylo Ren was an attempt to exploit his former student's weaknesses.
"[Luke] is basically tailoring this projection to have maximum effect on Kylo," Johnson explained to IGN. "He knows that Kylo's Achilles heel is his rage, and so that's why he kind of makes himself look younger, the way Kylo would've last seen him in their confrontation at the temple, and that's why he decided to bring Kylo's grandfather's lightsaber down there -- the lightsaber that Kylo screamed at Rey, 'that's mine, that belongs to me.'"
Luke's motivations make sense, because were he to appear to Kylo as the frail hermit he had become, Kylo might not have considered Luke a threat. Additionally, the younger appearance is the visage most familiar to Kylo, possibly enraging him further over the idea that Luke looks as strong as ever in the years since his exile.
Johnson's comments also shed light on how a Force projection works, as audiences had never seen this ability demonstrated. It was unclear just how much Luke could control his appearance, with Johnson's comments confirming the amount of control Luke had over the projection.
A confusing point about the lightsaber is that, earlier in the film, Kylo and Rey struggled over the saber, resulting in its destruction. Johnson noted that, while the audience knew what had happened, Kylo wasn't necessarily aware of it.
"We as an audience saw that... The truth is, we see the lightsaber split in half -- Kylo sees a blinding flash of light and is knocked unconscious, and then Rey takes the lightsaber away before he wakes up," Johnson pointed out. "So if you really want to dig into it and get an explanation, you can say that he doesn't 100 percent know what happened to the lightsaber."
The film also depicted a flashback in which Luke used the green lightsaber he constructed, yet never answered the question of that lightsaber's fate.
Perhaps we'll learn more about Luke's green lightsaber when Episode IX debuts on December 20, 2019.
The Last Jedi is in theaters now.