Genre and place in the book. The thirteenth passage is a simile-precept on the exercise of EXERCISE"keeping ready": as a surgeon keeps his instruments to hand, so keep your δόγματα ready. After the positive-methodological run (the programme 03-09, the "hold to the few" 03-10, the technique of definition 03-11, the formula of the good life 03-12), 3.13 supplies the equipment of that practice — the famous medical comparison. A doctrine on the readiness of doctrines.

Structure.

1. The simile. Physicians always keep their instruments (ὄργανα) and steel knives (σιδήρια) EXERCISEπρόχειρα — "ready to hand" — for the sudden needs of treatment (τὰ αἰφνίδια τῶν θεραπευμάτων).
2. The application. So too keep your δόγματα ready (ἕτοιμα) — for two ends: (a) to "know things divine and human" (τὰ θεῖα καὶ ἀνθρώπινα εἰδέναι) — the classic definition of wisdom; (b) to do everything, even the smallest (πᾶν καὶ τὸ μικρότατον), mindful of the DOGMAbond (σύνδεσις) of the two with one another.
3. The reason. You will do nothing human well without referring it up (συναναφορά) to the divine — and conversely (οὔτ’ ἔμπαλιν): the human and the divine mutually ground each other.

Key analyses.

• πρόχειρα / δόγματα ἕτοιμα — the exercise of EXERCISEprokheiron. The δόγματα are the short, memorisable fundamental rules of the Stoic life (e.g. "only virtue is good," "the present is all"), to be kept ready like a surgeon's scalpel against the sudden "needs" of life (αἰφνίδια — the unexpected blows). The image of the physician's kit: philosophy is therapeutic, and the doctrines are its instruments.
• The medical metaphor — philosophy as the medicine of the soul. A Stoic-Cynic commonplace (cf. Chrysippus' "therapy" of the passions; Cicero Tusc. III): the doctrines are surgical tools, the sudden cases are the impressions/blows, readiness is trained habit. The word σιδήρια ("irons," steel blades) underscores the sharpness of the instrument.
• τὰ θεῖα καὶ ἀνθρώπινα — "things divine and human." The standard ancient definition of wisdom/philosophy: σοφία = "the knowledge of things divine and human" (ἐπιστήμη θείων τε καὶ ἀνθρωπίνων; cf. Cicero, Seneca, SVF). Marcus invokes it: the dogmata furnish knowledge of both orders.
• σύνδεσις / συναναφορά — the bond and the upward-reference. The core claim: the divine and the human are interconnected (σύνδεσις), so every act (even the smallest) must be done with reference (συναναφορά) to the divine; you cannot do the human well in isolation from the divine, nor the reverse. This is DOGMAthe unity of the cosmos (the interweaving of all) applied to ethics: a human action is well done only when referred up to the cosmic-divine order. Physics grounds ethics. Cf. "all things are interwoven with one another" (Med. 7.9; 6.38; 4.40 — the one living being).
• πᾶν καὶ τὸ μικρότατον — even the smallest. Nothing is too trivial to be referred to the divine bond: the whole of life, down to its small change, lived under the doctrines.

The disciplines. The dogmata-ready (EXERCISEprokheiron) is the equipment of the whole practice. The leading one here is action (doing everything, even the smallest, mindful of the bond; "εὖ πράξεις" — you will act well). The secondary is assent (the dogmata as ready knowledge/judgement of the divine and human). At the same time, "knowing the divine" and "referring to the divine" ground ethics in physics — the basis of the discipline of desire (consent to the cosmic order). 3.13 is about the theoretical equipment (δόγματα) that underwrites all practice.

Stylistics. The extended medical simile (Ὥσπερ… οὕτω). The concrete surgical vocabulary (ὄργανα, σιδήρια, αἰφνίδια θεραπευμάτων). The chiastic close (οὔτε the human without the divine… οὔτ’ ἔμπαλιν — neither the human without the divine, nor the reverse). The totalising "πᾶν καὶ τὸ μικρότατον."

Parallels. δόγματα kept ready / the equipment — Med. 3.11; 4.3 (the retreat into oneself carrying the dogmata); 7.63; 9.42; 11.18; EXERCISEprokheiron; Epictetus Ench. (the "handbook" itself as a πρόχειρον). Philosophy as physician — Med. 5.9; Chrysippus' "therapy" of the passions; Cicero Tusc. III. "Things divine and human" (the definition of wisdom) — Cicero Tusc.; Seneca Ep. 89; SVF. The interweaving of all — Med. 7.9 (πάντα ἀλλήλοις ἐπιπέπλεκται); 4.40; 6.38; DOGMAunity-of-cosmos.