Ezekiel 25:15-17. God says that because the Philistines acted revengefully and "took vengeance with malice of heart to destroy in never-ending enmity", therefore he shall stretch out his hand against them. God will cut off the Cherethites (executioners and probably mercenaries) and destroy the rest of the sea coast. He will execute great vengeance upon them with wrathful chastisements. This will all be so that they know that he is the Lord.

I am not sure what the Philistines did this time, I did not go back and read what came before this, but I do know, because the passage tells us, that their actions were guided by "vengeance with malice of heart." It is interesting because later God says his own actions are for vengeance, but his are with chastisement in mind, not revenge. So because the Philistines vengeance was done with revenge in mind and malice in heart, they deserve punishment. Instead of seeking justice they sought to inflict pain on their enemies for the sake of seeing them hurt; that is, with malice.

God will never treat his anyone this way. The wrath and vengeance that he allows to befall us is always with justice and chastisement in mind, never with malice. This is a lesson on how much motivations matter. The same actions can be right and just or they can be evil and wicked, it really depends on the state of our hearts and minds in doing them.