Supreme Irony

Then they led Jesus from Caiaphas into the praetorion; and it was early. And they did not enter into the praetorion, in order that they might not be defiled but would be able to eat the passover.
--John 18:28

The efforts of Jesus' accusers, far from keeping them pure, were not only sinful but also the very thing that led to the ultimate passover sacrifice, a passover that, tragically, did not avail for them - because they were not, by faith in this passover, made pure. It was their wrongheaded attempt to be pure that defiled them.