Therefore I have cut them to pieces with the prophets; I killed them with the words of my mouth. Your judgments are like a flash of lightning.
Both meanings are inherent in the verse itself.  Of course, God had already "hewn" and "slain" with reference to his chosen people, and the prophets and their messages were the instruments through which this was done.  If the reference is only to what is past, then it still stands as an example of what God will continue to do to his rebellious children; and if the passage is prophetic and pertains to the future, then the certainty of its fulfillment is attested by the examples provided by God's past actions.  Inasmuch as Israel and Judah at this time were both yet standing, and in the light of the approaching doom and captivity for both, it is perhaps better to take the verbs here as prophetic past tense, pertaining to the future.