Yahweh is telling Ezekiel to speak to the mountains as if they were people so that the people of Israel would hear the words and know that Ezekiel's words were for them. (See: [[rc://en/ta/man/translate/figs-apostrophe]])
This is an idiom that is used to introduce something that God told his prophets or his people. See how you translated this in [Ezekiel 3:16](../03/16.md). AT: "Yahweh spoke this message" or "Yahweh spoke these words" (See: [[rc://en/ta/man/translate/figs-idiom]])