This ended up being more like a Top 7 Most Important Exchanges thing for me. Oh well.
Barret: "Yo! This your first time in a reactor?"
Cloud: "No. After all, I did work for Shinra, y'know."
Barret: "The planet's full of Mako energy. People here use it every day."
[Cloud shrugs]
Barret: "It's the life blood of this planet. But Shinra keeps suckin' the blood out with these weird machines."
Cloud: "I'm not here for a lecture. Let's just hurry."
Barret: "That's it! You're comin' with me from now on."
[A few seconds later]
Barret: "Little by little the reactors'll drain out all the life. And that'll be that."
Cloud: "It's not my problem."
Barret: "The planet's dyin', Cloud!"
Cloud: "The only thing I care about is finishin' this job before security and the Roboguards come."
—Barret and Cloud in the first mako reactor
Exposition that establishes everything we need to know about AVALANCHE, Shin-Ra, SOLDIER (Barret a few seconds earlier: "Ex-SOLDIER, huh? Don't trust ya!") and the overall plot at this point in the game. It also firmly establishes the kind of dickish behavior we can expect out of Cloud for a while, and the dynamic we can look forward to between he and Barret.
Rufus: "So... So Sephiroth was actually here. ...By the way. Who are you guys?"
Cloud: "I'm Cloud, former SOLDIER First Class!"
Barret: "I'm from AVALANCHE!"
Tifa: "Same here!"
Aeris: "...a flower girl from the slums."
Red XIII: "...a research specimen."
Rufus: "What a crew. Well, I'm Rufus. The President of Shinra, Inc."
Barret: "You only President, 'cause yer old man died!"
Rufus: "That's right. I'll let you hear my new appointment speech.
...Old man tried to control the world with money. It seems to have been working.
The population thought that Shinra would protect them.Work at Shinra, get your pay. If a terrorist attacks, the Shinra army will help you.
It looks perfect on the outside.
But, I do things differently.
I'll control the world with fear. It takes too much to do it like my old man.
A little fear will control the minds of the common people. There's no reason to waste money on them."
Tifa: "He likes to make speeches just like his father."
[Cloud turns to Barret]
Cloud: "Get outta this building with Aeris!"
Barret: "What?"
Cloud: "I'll explain later! Barret! This is the real crisis for the Planet!"
—Rufus's introduction following his father's murder
Not only does this present Rufus to us along with a somehow more threatening Shin-Ra, but it also lets us know lets us know — in the wake of losing Jessie, Biggs and Wedge — who our motley crew for this game is actually going to be.
As significantly, it shows us that the return of Sephiroth is an event that will make for a different game than the one we thought we were playing.
Aeris: "How do you intend to become one with the Planet?"
Sephiroth: "It's simple.
Once the Planet is hurt, it gathers Spirit Energy to heal the injury.
The amount of energy gathered depends on the size of the injury."
[He stabs his sword into the floor]
Sephiroth: "...What would happen if there was an injury that threatened the very life of the Planet?
Think how much energy would be gathered!"
[He pulls his sword back out]
Sephiroth: "Ha ha ha. And at the center of that injury, will be me.
All that boundless energy will be mine.
By merging with all the energy of the Planet, I will become a new life form, a new existence.
Melding with the Planet... I will cease to exist as I am now...
Only to be reborn as a 'God' to rule over every soul."
Aerith: "An injury powerful enough to destroy the Planet?
Injure... the Planet?"
Sephiroth: "Behold that mural. The Ultimate Destructive Magic... Meteor."
—Sephiroth emulates his favorite "James Bond" villain
In addition to showing off Seph being intimidating, this tells us what game we are actually playing, and what the rest of the plot will center around.
"...Shut up.
The cycle of nature and your stupid plan don't mean a thing.
Aeris is gone.
Aeris will no longer talk, no longer laugh, cry...... or get angry......
What about us...... what are WE supposed to do?
What about my pain?
My fingers are tingling.
My mouth is dry.
My eyes are burning!"
—Cloud, while holding Aerith's body immediately after Sephiroth murders her
If you didn't know how you should feel in the instant Sephiroth's sword pierced Aerith's spine — and I'm sure a great many players didn't know for a good moment — you should have known at this point. I think Cloud spoke for a great many of us.
"Everyone, listen to me.
I'm Cloud, ex-SOLDIER, born in Nibelheim.
I came to settle up with Sephiroth.
I came here by my own free will... Or so I thought.
However... ...To tell the truth, I'm afraid of myself.
...There is a part of me that I don't understand.
That part that made me give the Black Materia to Sephiroth.
If you hadn't stopped me, Aeris might have been...
...There's something inside of me. A person who is not really me.
That's why I should quit this journey.
Before I do something terrible.
But I am going.
He destroyed my hometown five years ago, killed Aeris, and is now trying to destroy the Planet. I'll never forgive... Sephiroth.
I... I must go on.
...I have a favor to ask of you.
Will you all come with me?
...to save me from doing something terrible."
—Cloud, shortly after Aerith's funeral.
If there was any remaining doubt that Cloud had changed since the beginning, there no longer should have been.
Bugenhagen: "The knowledge of the Ancients swirling around here is telling me one thing.
The planet's in a crisis...
A crisis beyond human power or endless time.
It says, when the time comes, we must search for 'Holy'."
Cloud: "Holy?"
Bugenhagen: "Holy... the ultimate White Magic. Magic that might stand against Meteor. Perhaps our last hope to save the planet from Meteor.
If a soul seeking Holy reaches the planet, it will appear.
Ho Ho Hooo.
Meteor, Weapon, everything will disappear.
Perhaps, even ourselves."
Cloud: "Even us!?"
Bugenhagen: " It is up to the planet to decide.
What is best for the planet. What is bad for the planet.
All that is bad will disappear. That is all.
Ho Ho Hooo.
I wonder which we humans are?"
—Bugenhagen tells us how to save the world
This scene not only introduces the measure to stop Sephiroth, but it introduces the game's greatest philosophical question — one which can be asked in real life: "Are humans bad for the planet, and would it be sad if we were gone?"
Cloud: "What are we all fighting for? I want us all to understand that.
Save the planet... for the future of the planet... Sure, that's all fine.
But really, is that really how it is? For me, this is a personal feud.
I want to beat Sephiroth. And settle my past.
Saving the planet just happens to be part of that.
I've been thinking.
I think we all are fighting for ourselves.
For ourselves... and that someone... something... whatever it is, that's important to us.
That's what we're fighting for.
That's why we keep up this battle for the planet."
Barret: "You're right...
It sounds cool sayin' it's to save the planet.
But I was the one who blew up that Mako reactor......
Lookin' back on it now, I can see that wasn't the right way to do things.
I made a lot of friends and innocent bystanders suffer...
...At first, it was revenge against Shinra. For attackin' my town.
But now...... Yeah. I'm fightin' for Marlene.
For Marlene... For Marlene's future...
Yeah... I guess I want to save the planet for Marlene's sake..."
Cloud: "Go and see her. Make sure you're right, and come back.
All of you. Get off the ship and find out your reasons for yourselves.
I want you to make sure. Then I want you to come back."
Cid: "Maybe ain't none of us'll come back.
Meteor's gonna kill us all anyway. Let's just forget any useless struggling!"
Cloud: "I know why I'm fighting.
I'm fighting to save the planet, and that's that.
But besides that, there's something personal too...
A very personal memory that I have.
What about you all?
I want all of you to find that something within yourselves.
If you don't find it, then that's okay too.
You can't fight without a reason, right?
So, I won't hold it against you if you don't come back."
—As the team approaches the day of their showdown with Sephiroth for the life of the Planet
Perhaps the most honest speeches ever given by heroes. Made all the more heroic because they are flawed, they know this, and they don't believe themselves to be heroes. They're each just trying to protect something that's important to them.
This dialogue tells you that it's okay to be flawed; just do the best you can. If, at any point, you forgot why you wanted to see these people succeed, this reaffirms it. It's because they could be you.