Understanding the First Way requires understanding the realities that pre-classical physics were interested in but which classical physics cannot account for. I’ll give a sketch of the First Way and then point out how what is now called science can’t account for the physical reality that it’s based on.
In syllogistic form, the First Way is
Everything moved by another is moved by some first, unmoved mover.
Everything in motion is moved by another.
The major premise has its objectors, but most of the objections muddle quantity (a finite vs. infinite amount of movers) with quantity (the kind of mover that a moved thing relates to).
Newtonianism, along with all science to this day, denies the minor premise, though in a different way than is usually thought: Neither can make sense of that-which-is-in-motion (TWIM). Newton carved out a very important place for the active cause of motion (force, quantity of motion, etc), and later theories developed and divided this into different ideas like energy, but they never specified the TWIM it acted on. Force acts on bodies, but not all bodies are TWIMs since body both conveys and receives force.
We can’t add TWIM to science since its absence is structural. Science is quantitative and so requires symmetries, but the relation between force/energy and TWIM is asymmetrical. Science can’t account for the reality of the force-TWIN relation any more than it can account for the reality of time, which Newton defined out of nature (true time was mathematical and impossible to instantate) which Einstein denied altogether with a Parmenidean block universe, and to which entropic accounts deny any necessary asymmetry.
At the moment science is more bothered by its inability to account for the asymmetry of time than of Energy-TWIM, though, if I’m right, it’s incapable of accounting for the reality of either. But it is just these asymmetries that pre-classical physics was most of all interested in. They were interested above all else in becoming, causality, action-passion, the reality of TWIM, and the order of proceeding from some principle. It’s by focusing on the reality of these things that one sees the sort of physics that gives rise to a cosmological argument.