diastellō

The lexica and word-study literature (BDAG; LSJ; Louw-Nida 33.323; Rengstorf, TDNT 7:588-599; Silva, NIDNTTE 4:342-45; Moulton-Milligan) trace διαστέλλω from a concrete classical sense (draw apart, distinguish, define precisely) into the dominant Koine sense of issuing a formally articulated, binding directive. By the Hellenistic period the middle voice is near-technical administrative vocabulary in the papyri for orders, land-registration, and banking drafts, so a first-century reader heard the register of magistrates and officials. In the Septuagint the verb renders chiefly בדל Hiphil (separate clean from unclean, Lev 10:10; 11:47) and, decisively for the New Testament, זהר Hiphil (warn/charge) in the watchman oracles of Ezek 3:18-19 and 33:7-9, which supplies the "solemn charge" register. In the New Testament the imperatival sense is uniform: Louw-Nida glosses it as "to give an order involving special explicitness and seriousness." Mark's five uses (5:43; 7:36 [twice]; 8:15; 9:9), all middle voice, form a lexical signature for emphatic authoritative commands and stand in a deliberate distributional split with ἐπιτιμάω, which Mark keeps for rebuking demons and Peter; Marcus (Mark 1-8, AYB), Yarbro Collins (Mark, Hermeneia), and France (NIGTC) all note this. Matthew's substitution of διεστείλατο for Mark's ἐπετίμησεν at 16:20 softens "rebuked" into "gave strict orders." Acts 15:24 uses the verb in its native epistolary and juridical register. At Hebrews 12:20 the substantivized present passive participle τὸ διαστελλόμενον means "the injunction / what was commanded" (closest parallel 2 Macc 14:28, τὸ διεσταλμένον); because LXX Exod 19:12, 23 uses ἀφορίζω, the Hebrews author is paraphrasing Sinai in his own high style, and commentators (Attridge, Ellingworth, Lane, Koester, Cockerill) agree the primary value is "what was commanded," with the etymological "boundary" nuance at most a stylistic coloring. Whether that older "distinguish/separate" nuance is exegetically live in the New Testament is disputed: the reference tradition presents a coherent developmental account, while modern critical commentators generally treat it as inert background outside Levitical and Ezekielian citations.