Caiaphas's statement is one of political expediency. Better that Jesus be done away with than that the Romans bring down military might on the Jews (or, at least, take away the power and privileges of the Jerusalem elite). That's what is meant by "better that one man should die for the nation." But Caiaphas spoke more than he knew. Jesus' death on the cross was not only "for the nation," but for the whole world. The "for" here points to the possibility of salvation that his death and resurrection create.