Such questions were part of a classical education, and in the past, no person with a university degree would not have had at least a basic speculative grasp of the subject. To respond, I would first want to make a few distinctions, as the language in the essay is muddled. I distinguish between three classes of acts that human beings can perform, namely, theoria, praxis, and poiesis.

1. theoria concerns acts that aim at knowledge, understanding, and wisdom; the aim is truth for its own sake

2. praxis concerns acts performed for their own sake; these are the primary subject of ethics, the practical philosophy

3. poiesis concerns acts of production where the end is distinct from the act that produces it as an effect

Paul claims that "[t]he most impressive thing humans can do is to think. It may be the most impressive thing that can be done". I agree that "thinking", or precisely the capacity for intentionality, abstraction of concepts, and the ability to reason about them (to which I would add the capacity to choose between apprehended alternatives) is, indeed, the most impressive and indeed most distinctive thing human beings are capable of. These constitute our rationality. However, what is the highest expression of this capacity? Paul claims that "the best kind of thinking, or more precisely the best proof that one has thought well, is to make good new things". This is confusing, as "the best kind of thinking" and "the best proof one has thought well" are talking about two different things. It's not clear what exactly the point here is in relation to the prior claim. Are we talking about the best kind of thinking or the best proof of having though well? And what about it?

"So what should one do? One should help people, and take care of the world. Those two are obvious. [...] Taking care of people and the world are shoulds in the sense that they're one's duty, but making good new things is a should in the sense that this is how to live to one's full potential."

Paul says such things are "duties" and that they are "obvious". Perhaps they are, in some sense, or perhaps these are hazy cultural attitudes he has absorbed that may not be obvious elsewhere, whether true or not. But what is the basis for such duties? What is their explanation? What is the basis of the good? Of morality? Of the normative (the "shoulds")?

The reason I harp on this point is because had Paul had a basic grasp of something like virtue ethics, he would have found that human nature is the foundation and basis for the objective good and thus for objective morality. He would have found the key that could systematically reconcile and explain and relate all these seemingly arbitrary "shoulds" he lists. He would have a basis for evaluating the place of theoria, praxis, and poiesis in the context of human nature, the good life, and the end of human life (its ultimate good).

We could then answer questions like "what is the best expression of human rationality?" Is it production as in poiesis? Or praxis? Or perhaps theoria? I claim it is theoria, and this does nothing to diminish the importance and the good of praxis or poiesis. They simply are not the highest expression of human rationality. They play supporting roles methodologically (and this is where Paul's comment about "proof of one has thought well" can enter the discussion), but they are not the end.

"There was a long stretch where in some parts of the world the answer became "Serve God," but in practice it was still considered good to be wise, brave, honest, temperate, and just, uphold tradition, and serve the public interest. [...] for example by saying, as some Christians have, that it's one's duty to make the most of one's God-given gifts. But this seems one of those casuistries people invented to evade the stern requirements of religion: you could spend time studying math instead of praying or performing acts of charity because otherwise you were rejecting a gift God had given you."

Why is "serving God" construed as distinct from "wise, brave, honest, temperate, and just" and so on? Why can't these be part of what it means to "serve God"? Why are we setting them in opposition as if they were in competition with one another rather than one and the same thing? Apparently, Paul is unaware of the parable of the talents in Matthew's gospel, or the five tasks given Mankind in Genesis by which Mankind better participates in the life of the Trinity, let alone the metaphysical "obviousness" of this being the case. The demonstrated grasp of "religion" in general (if we may even speak of it in general in any meaningful way) and "Christianity" in particular leave much to be desired, to put it mildly. I feel as if I'm reading the superficial tropes of a lazy observer rather than a sound grasp of the basics.

If anything, as Stanley Jaki among others argue, the reason why we saw an explosion of sustained scientific progress and techne in the West is because it follows from Christian principles, like the notion that all of the created order is inherently and totally intelligible (I would claim best expressed in John 1:1); that human beings are capable of grasping this intelligible reality (rooted, I would say, in the Imago Dei); the notion of the logos spermatikos; the distinction between creator (first causality) and created (second causality); the notion that human beings are "co-creators" (or "sub-creators", to use Tolkien's term) cooperating with God in the work of creation; and so on. These provide strong motivations to pursue this kind of work in a sustained and intense fashion. If you don't believe that the world is rational, that human beings can understand it, that it is somehow evil to investigate it, that religious texts are the only source of human knowledge (or even epistemically primary), that such texts can contradict truths known by unaided reason, that effort is futile and pointless, then you're not going to accomplish much.

"But there's nothing in it about taking care of the world or making new things, and that's a bit worrying, because it seems like this question should be a timeless one. [...] Obviously people only started to care about that once it became clear we could ruin it."

Obviously? I seem to recall Genesis giving men the authority of stewardship over the earth. I don't think the ancients doubted they could ruin the earth (ask a farmer), even if they did not know the scale at which we could eventually do so, but then this is not a matter of having or lacking said care, but a matter of prudential application of care.

"The traditional answers were answers to a slightly different question. They were answers to the question of how to be, rather than what to do."

Doing is act and being is act. Doing has as its ultimate end being, or else it is unintelligible. They are not opposed.

"Archimedes knew that he was the first to prove that a sphere has 2/3 the volume of the smallest enclosing cylinder and was very pleased about it. But you don't find ancient writers urging their readers to emulate him. They regarded him more as a prodigy than a model. [...] his contemporaries would have found it strange to treat as a distinct group, because the vein of people making new things ran at right angles to the social hierarchy."

I don't know what this means. He maintained relations with other scholars. Some scholars and philosophers ran their own schools (Plato, Aristotle, Pythagoras, etc), some did not.