Luke's neat "trick" at the end of Last Jedi, and consequences?

Question

How does Luke do this towards the end of the "Last Jedi"? (Some viewers are calling it a "parlor trick" online, and I think it's an apt expression.)

We see Luke coming to the last Resistance holdout in Crait, talking to Leia, putting the gold charms from the Falcon in her hand, and then going out to face the First Order alone. He survives a massive barrage of firepower, and then faces Kylo Ren face to face, deftly avoiding Kylo's strikes. While he takes on Kylo Ren and the First Order, the Resistance is able to escape.

But at the end of this, we see that:

It's a projection. The real Luke is still on Ahch-To, and he's projecting a "hologram" of himself across the universe.

And after it disappears, we see:

The real Luke coming out of meditation, sweaty and panting on Ahch-To (from the effort in projecting his hologram across the universe, I'm guessing), and falling off his levitation and meditation rock in pain.

He later wakes up, sees the two suns (similar to his first introduction scene over 30 years ago in "A New Hope") and then literally just disappears (like Yoda did at his death in "Return of the Jedi".)

How did he do this? And did he do it this way (as opposed to facing the First Order and Kylo Ren directly) so that he could inspire hope among a new generation of Resistance fighters and Jedi? Towards the very end of the movie, we see:

On Canto Bight, a bunch of kids are telling each other stories of how the amazing Jedi Master Luke Skywalker took on and survived the firepower of an entire army of the First Order (while allowing the Resistance to escape.) The story inspires the kids, and the film ends with one of the kids stepping outside the room, using the Force to move a broom into his hand, looking out into space and seeing a spaceship speed across the stars, eyes bright with hope.

Answer 1

I propose a different solution to the above below.

Luke doesn't die from his projection. Luke gives himself to the Force, like Obi-Wan did.

I had originally saw Machavity's reasoning that Luke strained so hard that it had killed him. This seemed likely because at the time I distinctly recall seeing him splayed across the rock and then him disappearing. But this isn't what happens.

While, Luke is splayed across the rock after preforming his feat, this isn't what kills him, Luke is later seen cross-legged, meditating, like he was before. This is all while he connects for the final few times with Leia and Rey, and projects the dice for Kylo.

After Kylo picks up Han's Sabacc dice, Luke, while still meditating becomes one with the Force and fades into it. Luke has fulfilled his duty as a master and successfully trained a padawan (albeit indirectly) to become the next Jedi. Although his lessons may have been reasons for the ending of the Jedi, they also taught how to be a good Jedi.

This all mirrors Luke's earlier talks about how he was a Legend, but that the Jedi Order leads to failure and humiliation. While Luke was a hero to the people who wanted to be free of the tyranny, he had failed in protecting those people, until Rey brought him back to the light and out of exile. Luke re-ignited the spark that will free the Galaxy and in turn redeemed himself in terms of the Force.

Luke, like Obi-Wan is seen departing into the Force on his own terms. After having trained the next era of Jedi, they willingly give themselves to the force to become a Force ghost.

Answer 2

The clear answer from the movie is that

Luke Skywalker, Jedi master, threw his entire being into focusing a projection of himself, via the Force, which either killed him, or made him a Force Ghost

There's nothing canon that comes close to that. It is, literally, the greatest canon feat we've seen (to date) from any Force user (and I'd expect nothing less from a man who was already a legend). Now, in Legends, we saw something similar (spoilered since it would give away the previous spoiler)

Dorsk 81 does a pretty massive Force push that kills him in the process.

There's nothing canon suggesting what the limits of a Jedi's power are.

So why do it that way?

Luke didn't go with Rey. While he had his X-wing, it might not have worked, having been submerged for so long (and he didn't have R2D2 to help fix it). Then you have the problem of getting through the First Order ships. Might be easy for a Jedi master, but might have cost precious time. And, finally, there was a dire need. The entire Rebellion was now on the line. Their extermination would have meant total First Order domination. As was noted several times, hope was riding on this ragged crew of people. There likely wasn't time for Luke to physically travel there, even if he had a functional ship.

Ultimately, Luke did it that way to buy time, the only thing he could do. Kylo Ren took the bait. Luke did what good heroes do. He did what Obi-Wan did. He sacrificed himself.

The final scene cements Luke Skywalker into a legend. The man who stopped the Empire, and then (for one last time) the First Order. And then, we see kids retelling stories of Luke Skywalker, Jedi master.

But what's really astonishing is something so subtle it was easy to miss. That boy who goes outside to sweep? If you look closely, you'll notice he grabs the broom by reaching out through The Force. He then, at the end, hold the broom like a lightsaber. The ramifications are clear: the Jedi are not dead. Not by a long shot. Luke may be gone, but his fire still burns.

Answer 3

Luke over-exerted himself with the Force performing the Jedi technique of Similfuturus.

This Jedi had not moved since dawn. During that time, the mountain had quaked. A cliff had crumbled. The twin suns had begun to set. The moon had gone on the rise.

It had taken all his strength to do what he had done. The salt lines of tears on his face showed the incredible strain. Now that it was done, he could enjoy a few last breaths from the island that had been his home.

_{^{Last Jedi: Junior Novelisation}}

His efforts drained his "essence". Ben Kenobi then encouraged him to become one with the Force.

On the ledge overlooking the sea, Luke Skywalker floated a few centimeters above the stone. Pebbles hovered around him. His eyes were closed and his legs crossed. His face was strained, and beneath his gray beard the tendons of his neck stood out. Tears streamed down his face as he poured his strength, his very essence, into the Force.

Behind him the peak shuddered, shedding dust and chunks of debris.

...

Luke heard the wail of the wind and the cries of the birds. He heard his own faltering breaths as he struggled to get up, and the rhythmic thumping of his heart in his chest.

And he heard a familiar voice. Maybe it was real, or perhaps it was just in his memory.

Let go, Luke.

He did and his body faded away, leaving the ledge empty. In the spot where he had been, the Force rippled and shivered. But a moment later this disturbance was lost amid countless other currents of an autumn evening on the island, and the Force continued as it always had, luminous and vast and eternal.

_{^{The Last Jedi: Official Novelisation}}

And there's a nice description of the act (and its consequence) in the Rise of Skywalker: Visual Dictionary.

Luke Skywalker takes to the battlefield and is seemingly untouchable by First Order artillery. Kylo Ren rages against his former master, unable to strike Skywalker down. In truth, Luke's presence exists only in the Force, a projection through a Fallanassi technique chronicled by ancient Masters in the sacred texts as Similfuturus. This discipline requires extreme concentration and focus, as Luke essentially pours his living Force presence into the all-encompassing cosmic Force, bridging incredible distances.

The transition is so complete that Luke gives his all into the Force, finding serenity in this final mortal moments and becoming one with the great beyond. This is inexplicable to First Order witnesses, who see an indestructible Jedi Master vanish before their eyes.