Robo Bobo - Difference between perished and destroyed:
You perish. Someone doesn't "perish you." You pass away.
Destroyed means someone kills you.
Well, yes, but we need to remember that, from the historical perspective, Jesus was an apocalyptic Jewish preacher. He did believe that if you didn't have (not "exercise") faith in God, you'd die. You'd be killed in the upcoming Armageddon. He did believe that—except that he believed the Armageddon would come in his lifetime or shortly after his death. The same goes for Paul. Therefore, in the context of Jesus' being an apocalyptic preacher who believed that God would establish his own kingdom on earth and destroy all other kingdoms, he would probably mean "perish" as in... "God will kill you if you don't believe in him."
Additionally, keep in mind that gJohn is the least reliable of the gospels in the New Testament.