Quote 1
Boggs forces the Holo into my hand. His lips are moving, but I can't make out what he's saying. I lean my ear down to his mouth to catch his harsh whisper. "Don't trust them. Don't go back. Kill Peeta. Do what you came to do." (20.18)
Who should Katniss "trust"? Boggs's last words are a warning to her that she shouldn't "trust" anyone. But can she even trust <em>him</em>? Everyone and anyone could be playing her false and be looking out for their own gains. She can't tell who "them" refers to or what manipulations Boggs was trying to make her aware of.
Quote 2
"It's not that simple," he [Boggs] shoots back. "We were in no position to launch a counterattack until recently. We could barely stay alive. After we'd overthrown and executed the Capitol's people, only a handful of us even knew how to pilot. We could've nuked them with missiles, yes. But there's always the larger question: If we engage in that type of war with the Capitol, would there be any human life left?" (6.63)
Is there ever any right answer in a war? Boggs is explaining to Katniss how, even though his side had the means to take down the Capitol, doing so would come at too high a price. Are people willing to destroy so many innocent lives in order to effect real change? Even so, it's hard for Katniss to accept that, in the meantime, atrocities like the Hunger Games have been allowed to continue.
Quote 3
"If your immediate answer isn't Coin, then you're a threat. You're the face of the rebellion. You may have more influence than any other single person," says Boggs. "Outwardly, the most you've ever done is tolerated her." (19.13)
Boggs clarifies for Katniss the fact that she's in terrible danger from Coin – that Coin may very well want her dead. Katniss wields too much power for Coin's liking, and has the potential to destabilize Coin's position at the top. Dead, though, Katniss could be used for Coin's cause. So, yeah, Katniss has to watch her back.