I know what I have to do, but I don't know if I have the strength to do it.
This is perhaps the most important quote in the film. To provide some context, it occurs when Kylo Ren has finished fighting Rey on the ocean platform and is deciding whether or not to give up the Sith and the Dark Side. Eventually, Kylo decides to throw his lightsaber into the ocean and gives up on the Sith and the Dark Side. In essence, this is Kylo's turning point and signals a massive change in his attitude and actions.
Obi Wan Kenobi: These are you final steps, Rey. Rise and take them.
Anakin Skywalker: Rey.
Ahsoka Tano: Rey.
Kanan Jarrus: Rey.
Anakin Skywalker: Bring back the balance, Rey, as I did.
Luminara Unduli: In the night, find the light, Rey.
Mace Windu: You're not alone, Rey.
Yoda: Alone, never have you been.
Qui-Gon Jinn: Every Jedi who ever lived, lives in you.
Anakin Skywalker: The force surrounds you, Rey.
Aayla Secura: Let it guide you.
Ahsoka Tano: As it guided us.
Mace Windu: Feel the force feeling through you, Rey.
Anakin Skywalker: Let it lift you.
Adi Gallia: Rise, Rey.
Qui-Gon Jinn: We stand behind you, Rey.
All of these characters have played parts in the previous eight films in the Skywalker Saga - from Obi Wan Kenobi to Qui-Gon Jinn - and tell Rey these things while they are in the form of Force Ghosts. They are meant to give Rey the strength to face the evil Emperor Palpatine, who is bent on ruling the galaxy yet again.
In the event I don't make it back, I want you to know you've been a real friend, R2. My best one, in fact.
This is a solemn and emotional line which is meant to signal the end of C3PO's life. Although C3PO's life doesn't end, it is meant to make viewers feel sad, as one of the best and most famous sagas in film history is coming to an end.
