By this term [spiritual exercises], I mean practices which could be physical, as in dietary regimes, or discursive, as in dialogue and meditation, or intuitive, as in contemplation, but which were all intended to effect a modification and a transformation in the subject who practiced them. The philosophy teacher’s discourse could also assume the form of a spiritual exercise, if the discourse were presented in such a way that the disciple, as auditor, reader, or interlocutor, could make spiritual progress and transform himself within.Pierre Hadot What is Ancient Philosophy?, 6
So when Epictetus offers a version of the argument for God from design, what he means to do is make someone aware, not only of the existence of a mind behind the cosmos, but he means to help them become grateful to God for the universe and their experiences therein.
The ubiquity of spiritual exercises in the ancient world helps make sense of Jesus’ paradox of public piety. In Matthew 5:14-17, Jesus says to do good deeds publicly. In Matthew 6:1-18, Jesus says to hide your good deeds so thoroughly that they fade from conscious memory (Matthew 25:37-40). Which is it? If we take his first command in sequence to be a piority, Jesus means to say, “My kingdom should be a people of the sort that those who observe their public life wish to worship God.” But on the other hand, there’s a serious moral burden to bear when we are seen and praised for doing good deeds. And so Jesus commends as a spiritual exercise to conceal certain good deeds some or most of the time so that the God who sees what happens in secret will reward the believer rather than the watching public.
C.S. Lewis, while not relying on Hadot, saw this mode of thought in the writings of the ancients absorbed and reworded it in his book on how to read. In it, he distinguishes between the way the many and the few
The distinction can hardly be better expressed than by saying that the many use art and the few receive it. The many behave in this like a man who talks when he should listen or gives when he should take. I do not mean by this that the right spectator is passive. His also is an imaginativeC.S. Lewis An Experiment in Criticism III.19b-20a
activity;but an obedient one. He seems passive at first because he is making sure of his orders. If, when they have been fully grasped, he decides that they are not worth obeying—in other words, that this is a bad picture—he turns away altogether.
Literary art is a spiritual exercise proffered to the reader by the artist, and once truly understood, then it is used or not. Of course, this raises all sorts of questions about art that is meant merely to entertain or titillate without any definite end, but even such art is offering a vision of life to be accepted or rejected and which one subtly endorses more and more the more frequently he enjoys artworks of that sort.
Later authors, like Rene Descartes, employed even geometry as a spiritual exercise. Descartes thought that arts like Geometry and Philosophy existed for self-cultivation by which he meant,
…[D]eveloping the ability to allow the will to recognize and to accept freely the insights of reason, and not just following the passions or memorized patterns of actions. It meant essentially recognizing the limits of reason and willing not to make judgments about things beyond reason’s scope.Matthew Jones Descartes’ Geometry as a Spiritual Exercise, 53.
As far as I can tell, the utility of the concept of spiritual exercises for understanding education in general, ancient philosophy, and even the Biblical texts cannot be overestimated.