What is the theme of Chapters 7, 8, and 9 of The Outsiders by S. E. Hinton?

The theme of these chapters is that life is precious and it is more important to live it than to fight.

These chapters center around Johnny dying in the hospital and the rumble between the Socs and the greasers.  The two situations are juxtaposed for a reason.  Life is precious.  Johnny is wishing that he had lived a longer life, and the conflict between the greasers and the Socs robbed him of it.  It is pointless bloodshed.

Johnny’s death is a result of the fire at the church, where he was injured trying to save the children.  However, it was really caused by the Soc-greaser war.  If the two gangs were not constantly at odds, Johnny and Pony would never have been hiding in the church in the first place.  The fighting, and in this case killing, over territory and identity is pointless and needs to stop.

In the hospital, Johnny tells Pony that he was too young to die.

"I don't want to die now. It ain't long enough. Sixteen years ain't long enough. I wouldn't mind it so much if there wasn't so much stuff I ain't done yet--- and so many things I ain't seen. It's not fair. You know what? That time we were in Windrixville was the only time I've been away from our neighborhood." (Ch. 8) 

Johnny has a point.  He did not really get to live his life, and all for a really silly reason.  The Socs attacked him because he was a greaser, and they kept attacking him.  They were worried about territory and who was seen with who.  There was no actual conflict that would cause the fight in the park where Johnny killed Bob.  It was just gang fighting. 

Randy, who was in the park when Bob was killed, tells Pony that he is not going to the big Soc vs. Greaser rumble. 

"I'm sick of all this. Sick and tired. Bob was a good guy. He was the best buddy a guy ever had. I mean, he was a good fighter and tuff and everything, but he was a real person too. You dig?" (Ch. 7)

Randy also has figured out the pointlessness of the endless fighting and killing.  He realizes the importance of life and the value of putting the war behind them.  Two young people are dead, and for what?  If enough of the gang members came to the same understanding as Johnny, Pony, and Randy, the fighting would stop.