Defile the temple: In the past, Queen Athaliah was dragged out of the temple before she was executed. This was done so that her blood would not defile (make unclean) the holy place (2 Kings 11:15–16).
Now the situation was different. These idolaters were to be killed inside the temple. Their idolatry had already defiled it so deeply that nothing sacred remained there.
Without God’s holy presence, the building was no longer truly holy. Protecting its outer purity would have been an empty act