Objection: The First Way starts from some particular motion or change and concludes to a mover that is unmoved. But it only need to be unmoved with respect to that particular motion. If something gets heated up, it only requires something that isn’t heated up (like a fire). But it’s laughable to think that something that is only unmoved with respect to some particular motion could be called a divinity. All sorts of mundane natural things are unmoved in this way.
Response: Edward Feser apparently takes this objection as of great moment – in response to it he has to stipulate that The First Way reduces to a proof for creation from a background assumption of existence as such as an actuality. I disagree with this reading but take it as beside the point here. The simpler response is that while it is true that, say, some fire is unmoved in some respect to some particular heating up, the fire as such doesn’t explain the heating up. Fires can’t heat an object simply by existing – for then a fire in the my basement could heat something on the moon. These sorts of causes have to also be made proximate or local to their effects, which requires not just the fire but whatever brought it to the thing it’s heating or started it in the right area. The necessity of these auxiliary motions to a cause that is unmoved in some way ensures that a sufficient account of a natural cause can never be unmoved even with respect to a particular motion.
In the FW’s STA is targeting a primary, non-natural being. They describe ways that nature is caused. In the first, he takes nature as the mobile (and for all our snickering about Aristotle, we seem to agree with him on this. All fundamental units of physics are descriptions of his kinesis)