Thus says YHWH, the God of Israel: Write in a book all the words that I have spoken to you.
Jeremiah 30:2

Sometimes God tells a prophet to speak, sometimes to write, and sometimes to carve images into wood or hammer them into gold.

The medium is secondary to the message itself, but the medium also adds a layer of meaning. God chooses one method or another of delivering a prophecy for a reason, even if we don't know what the reason is.