The OT prophets spoke of the glories of the messianic age in the ‘garb’ of ideas and concepts that were familiar to them.
This is like when you watch an old movie that is about the future (like 2010: The Year We Make Contact) and from our perspective it’s vision of the future looks a lot like the time the movie was made. It is a very 80s-ish understanding of the future (all the way down to the men wearing high shorts). They described the future that way because that’s how 80s people understood the future.
Similarly, the prophets spoke of the future messianic age in ways that people of their time and space would understand them. Yet, because the Spirit inspired them, their words were reliable guides for God’s people, and not deluded projections