He simply said that he feels he did what he had to do. He never said he was happy he shot Martin. You likely wouldn't be able to grasp the God's plan part, but Christians feel that things that happen to them that are beyond their control are preordained by their higher power. He didn't make a judgment, he basically said Que Sera Sera.
I grasp it.. but I don't believe that can be used as an excuse. I believe God gave us free will. I don't believe killing this boy was the christian thing to do.
I don't either, but I don't believe that allowing a kid to beat you to death is particularly Christian, either. Zimmerman had in his possession, a tool he could use to save his life. In stead of shooting as soon as he was hit in the nose, he tried to escape, (scooting around) called for help and when the only person that could have actually done anything to stop Martin's assault, turned his back deciding to call 911 instead of coming to his aid, he did what he felt he had to do in order to save his life.
I'd be on the opposite side of this argument if Martin had punched Zimmerman and Zimmerman shot him from a standing position.
I believe Zimmerman was in fear for his life due to an unprovoked attack on his person that he could reasonable expect would conclude with him being dead or gravely injured.