How we cite our quotes: All quotations are from Star Trek III: The Search for Spock.
Quote #1
KIRK: U.S.S. Enterprise, Captain's personal log. With most of our battle damage repaired, we're almost home, yet I feel uneasy and I wonder why. Perhaps it is the emptiness of this vessel. Most of our trainee crew have been reassigned. Lieutenant Saavik and my son David are exploring the Genesis planet, which he helped create, and Enterprise feels like a house with all the children gone.
At the end of The Wrath of Khan, Kirk looks at the Genesis planet with a sense of hope and new life. But Kirk's view on life has become one of loneliness and lost purpose.
Quote #2
KIRK [on recording]: To fully understand the events on which I report, it is necessary to review the theoretical data on the Genesis device, as developed by Doctors Carol and David Marcus. Genesis, simply put, is life from lifelessness. It was the intention to introduce the Genesis device into a preselected area of a lifeless space body, a moon or other dead form. The device, when delivered, would instantaneously cause the Genesis effect. Instead of a dead moon, a living, breathing planet now exists, capable of sustaining whatever life forms we see fit to deposit on it.
Genesis returns in The Search for Spock, but like Kirk's joie de vivre, the script has been flipped on this life-granting symbol. In the Wrath of Khan, the device provided hope and new life. As we'll learn later, Genesis is unstable and serves as a symbol for how the truth of life and existence will forever be beyond the grasp of science.
Quote #3
SAREK: Because he asked you to. He entrusted you with his very essence, with everything that was not of the body. He asked you to bring him to us and to bring that which he gave you, his katra, his living spirit.
KIRK: Sir, your son meant more to me that you can know. I'd have given my life if it would have saved his. Believe me when I tell you, he made no request of me.
SAREK: He would not have spoken of it openly.
The katra is the Vulcan equivalent of the mind, soul, or essence. It is completely separate from the material world, and Spock's contains everything that is essentially Spock. It can also, apparently, be uploaded from on body to another.