The view from above. The passage opens with the classic EXERCISEview from on high: Asia and Europe are "corners" (γωνίαι) of the cosmos, the sea a drop, Athos a clod of earth, the present a point of eternity (στιγμὴ τοῦ αἰῶνος). The spatial and temporal shrinking lays bare the conclusion: "all is little, changeable, vanishing." The governing discipline is desire (to accept smallness and flux); the sustaining one is assent (to judge the source rightly).
One source. The second move goes from scale to origin: everything comes "from thence," from the common TERMruling principle (κοινὸν ἡγεμονικόν) — either directly (ὁρμήσαντα) or "by way of sequence" (κατ’ ἐπακολούθησιν, as a secondary consequence). This is Stoic cosmology: the single governing Reason-Logos is the source of all that is.
Theodicy. The climax is a hard thought: "the lion's jaws, and poison, and every harmful thing — like thorns, like mud — are DOGMAafter-products (ἐπιγεννήματα) of the venerable and beautiful." Even the dangerous and foul are not an alien admixture but by-products of a good whole. Hence the imperative of assent: do not form the TERMimpression (μὴ φαντάζου) that evil is alien to what you revere, but "reckon up the DOGMAsource of all" (ἐπιλογίζου). A providential optimism: particular "evils" are built into the goodness of the Whole.
Parallels. EXERCISEview-from-above — Med. 7.48; 9.30; 12.24 (the view from on high on ant-like bustle); 04-50 (the smallness of time); the doctrines of DOGMAunity and DOGMAprovidence; cf. the disjunction "providence or atoms" (04-27). The theodicy of harmful creatures — cf. Med. 5.8 (all is "prescribed" by the nature of the Whole, like a medicine).