You do not realise that it is better for you that one man die for the people than that the whole nation perish.”
“realize” (NIV) = “consider” (KJV) = dialogizomai = to reason it out, to reckon up your accounts. He is saying that they are incapable of working it out that this certain course of action is the best one to take.
“for you” = they are not concerned about what is right or wrong and they are not really concerned over the nation as a whole; their major concern is that their position as the privileged, ruling class is being threatened and his course of action will help to preserve that. McGarvey says of Caiaphas, “Expediency, not justice, is his law.” (TFG) It is ironic that instead of preserving their nation and their position, this very decision would lead to its destruction. This happened in 70 A.D., several years before the writing of John’s gospel, and Barclay observes that “all who read it would see the dramatic irony in the words of the Sadducees.”
Edersheim notes, “This was the last prophecy in Israel; with the sentence of death on Israel’s true High-Priest died prophecy in Israel, died Israels’ High-Priesthood. It had spoken sentence upon itself.” (Life ii, 326)