In chapter 1 of A Guide to the Good Life, William Irvine provides a good summary of the three components of Stoic philosophy and how they are interrelated:
“Zeno’s philosophy had ethical, physical, and logical components. Those who studied Stoicism under him started with logic, moved on to physics, and ended with ethics. … The Stoics’ interest in logic is a natural consequence of their belief that man’s distinguishing feature is his rationality.
Physics was the second component of Zeno’s Stoicism . Living, as they did, in a time without science, Zeno’s students doubtless appreciated explanations of the world around them. And besides providing explanations of natural phenomena, as modern physics does, Stoic physics was concerned with what we would call theology.
[Ethics] is concerned not with moral right and wrong but with having a “ good spirit,” that is, with living a good, happy life or with what is sometimes called moral wisdom.
By studying logic, [the Stoics] hoped to perform well one of the functions for which we were designed; namely, to behave in a rational manner. And by studying physics, they hoped to gain insight into the purpose for which we were designed.”
In the above, I would replace “theology” with “metaphysics,” though some Stoics clearly did talk about God.
Irvine then brings up the fact that the Stoics often explained the relationship among the fields of logic, physics and ethics by way of metaphors. Here is his favorite one:
They asserted, for example, that Stoic philosophy is like a fertile field, with “Logic being the encircling fence, Ethics the crop, Physics the soil.” 20 This metaphor makes clear the central role played by ethics in their philosophy: Why worry about the soil and why build a fence unless a crop will result?”
Another one, of course, is that of an egg (see picture), which I explained in more detail in this article in Scientia Salon.