How we cite our quotes: All quotations are from Star Trek III: The Search for Spock.
Quote #1
KIRK: No. More empty even than that. The death of Spock is like an open wound. It seems that I have left the noblest part of myself back there on that newborn planet.
Spock's choice to sacrifice himself and implant his katra into McCoy looms large over this film. In fact, this story is really about Kirk and his crew dealing with the consequences of that choice while Spock enjoys a staycation chillin' in McCoy's brain space.
Quote #2
VALKRIS [in Klingon]: Success, my lord, and my love.
KRUGE [in Klingon]: You will be remembered with honor. Fire!
Kruge can't make a decision that doesn't end in someone dying. It's like he has some kind of villainous death quota to meet. That's because, unlike Kirk, who makes choices based on what he feels is best for others, Kruge's choices stem from what is best for Kruge. Everyone else is incidental cannon fodder.
Quote #3
DAVID: Why don't we beam it up?
ESTEBAN: Oh, no, you don't. Regulations specifically state, "Nothing shall be beamed aboard until danger of contamination has been eliminated."
SAAVIK: Captain, the logical alternative is obvious. Beaming down to the surface is permitted.
ESTEBAN: If the Captain decides that the mission is vital and reasonably free of danger.
DAVID: Captain, please, we'll take the risk, but we've got to find out what it is.
SAAVIK: Or who.
Captain Esteban is a by-the-books leader. Every choice he makes is designed to skirt personal responsibility and place the burden on the rule book. In a universe where decisions need to be made quickly and consequences can be messy, this doesn't make Esteban the most effective of captains.
Quote #4
SULU: The word, sir?
KIRK: The word is no. I am therefore going anyway.
Kirk chooses to disobey a direct order from his superior officer. It's a pivotal choice in the film, and the remainder of the story is essentially a direct consequence of it.
Quote #5
STYLES [on the comm]: Kirk. If you do this, you'll never sit in the captain's chair again.
KIRK: Warp speed.
SULU: Aye, sir. Warp speed.
Styles reminds Kirk of one consequence of his choice. Kirk decides to keep on truckin' but this will only be the first of many consequences to come. Side note: Kirk will sit in the captain's chair again in Star Trek V but only after he saves every life on Earth with humpback whales. But it's not like he planned that unless…did he?
Quote #6
DAVID: I used protomatter in the Genesis matrix.
SAAVIK: Protomatter, an unstable substance which every ethical scientist in the galaxy has denounced as dangerously unpredictable.
DAVID: But it was the only way to solve certain problems.
SAAVIK: So, like your father, you changed the rules.
Like his father, David has made a choice and now must face the consequences. In this case, the realization that Khan only killed people because David managed to get Genesis to a working stage. Yet Genesis ultimately doesn't work. Bummer.
Quote #7
KIRK: My God, Bones, what have I done?
MCCOY: What you had to do. What you always do. Turn death into a fighting chance to live.
Another consequence of Kirk's choices is the destruction of his beloved Enterprise. While Kirk looks on in horror at what his actions have wrought, McCoy reminds him of another, more beneficial, consequence: They all got to live that much longer.
Quote #8
KIRK: You fool, look around you! The planet's destroying itself!
KRUGE: Yes, exhilarating, isn't it?
KIRK: If we don't help each other, we'll die here.
KRUGE: Perfect. Then that's the way it shall be.
Again, Kruge's decision is to get Genesis no matter the cost and this time that might include his own death. Got to give him credit: this Klingon knows what he wants.
Quote #9
MCCOY: Spock, for God sakes, talk to me. You stuck this damn thing in my head, remember? Remember? Now tell me what to do with it. Help me. [McCoy looks concerned.] I'm gonna tell you something that I never thought I'd ever hear myself say. But it seems I've missed you, and I don't know if I could stand to lose you again.
We always wondered why Spock chose to put his katra in McCoy when he had a perfectly good, unconscious Scotty nearby. In this scene, we see why. He knew McCoy would choose to do what was necessary to ensure his katra got back safety. They may argue all the time, but they're true spacebros in the end.