How we cite our quotes: All quotations are from Star Trek IV: The Voyage Home.
Quote #1
SPOCK: If memory serves, there was a dubious flirtation with nuclear fission reactors resulting in toxic side effects.
The first aspect of our world that gets criticized as "primitive" is nuclear energy. By talking about this technology as a specific historical phenomenon that came and went, Spock shows us that our current era is a mere blipon the historical radar.
Quote #2
SULU: San Francisco. I was born there.
MCCOY: It doesn't look all that different.
San Francisco is an important city in the future—it's the headquarters of the Federation. The crew knows the place well. But although it might seem similar now, our crew members are in for a big surprise.
Quote #3
KIRK: Many of their customs will doubtless take us by surprise. It's a foregone conclusion that none of these people have ever seen an extraterrestrial before.
Spock responds to Kirk's statement in the most amazing way possible—by ripping off a piece of his robe and fashioning it into a headband, which he uses to hide his pointy eyebrows and ears. It's actually a good look. That being said, Spock's physical features will be the least distressing thing about him to this primitive world.