"Don't grieve, Admiral."
These simple words are some of Spock's last as he's dying from radiation burns in the warp core of the Enterprise while fighting to save the crew during the Wrath of Khan. It is a curious choice of phrase.
Spock can't tell Kirk "I know you are hurting." He can't say "I did this because of my love for my captain and my crew." He can't let anyone know what he feels.
"I have been, and always shall be, your friend."
And an unlikely friendship, between passion and logic, the connection of reason with intuition. There's so much unspoken under what Spock says. Don't grieve -- not because I am telling you not to hurt; not because I am telling you not to care; because I know you care, I know you hurt, but I am telling you in the only way that I can that what I have done was logical; I made a choice to sacrifice for people because I, too, cared about them. So don't grieve, because it is not a pointless death or an empty death. It is a logical death, and if I could feel, I would tell you that it is the death that I chose because of my love for my crew and captain.
The final word to McCoy, the rival, who becomes the unlikely acolyte. A note which triggers McCoy's response later: "You know, he's not really dead, as long as we remember him." Because we all remember him. We remember the part of us that he touched, the part that lives on in our minds. In the case of McCoy this touch was literal. For the rest of us, though, it will live on through the experiences we shared.