Commentaries:
Robertson's Word Pictures (NT)
These take (toutouv paralabwn). Second aorist active participle of paralambanw. Taking these alone.
Purify thyself with them (agnisqhti sun autoiv). First aorist passive imperative of agnizw, old verb to purify, to make pure (agnov). See the active voice in James 4:8; I Peter 1:22; I John 3:3. It is possible to see the full passive force here, "Be purified." But a number of aorist passives in the Koin‚ supplant the aorist middle forms and preserve the force of the middle (Robertson, Grammar, p. 819). That is possible here. Hence, "Purify thyself" is allowable. The word occurs in Numbers 6:1 for taking the Nazarite vow. The point is that Paul takes the vow with them. Note agnismou in verse Acts 21:26.
Be at charges for them (dapanhson ep autoiv). First aorist active imperative of old verb dapanaw, to incur expense, expend. Spend (money) upon (ep) them. Ramsay (St. Paul the Traveller, etc., p. 310) argues that Paul had use of considerable money at this period, perhaps from his father's estate. The charges for five men would be considerable. "A poor man would not have been treated with the respect paid him at Caesarea, on the voyage, and at Rome" (Furneaux).
That they may shave their heads (ina curhsontai thn kefalhn). Note thn kefalhn, the head (singular). Future middle indicative of curaw, late form for the old curew, to shave, middle to shave oneself or (causative) to get oneself shaved. This use of ina with the future indicative is like the classic opwv with the future indicative and is common in the N.T. as in the Koin‚ (Robertson, Grammar, p. 984).
And all shall know (kai gnwsontai). This future middle indicative of ginwskw (cf. akousontai in verse Acts 21:22) may be independent of ina or dependent on it like curhsontai, though some MSS. (H L P) have gnwsin (second aorist subjunctive, clearly dependent on ina).
Of which (wn). Genitive plural of the relative a (accusative) object of the perfect passive verb kathxhntai (cf. verse Acts 21:21 kathxhqhsan) attracted into the case of the omitted antecedent toutwn. The instruction still in effect.
But that thou thyself walkest orderly (alla stoixeiv kai autov). Stoixeiv is an old verb to go in a row (from stoixov, row, rank, series), to walk in a line or by rule. In the N.T. only here and Galatians 5:25; Romans 4:12; Philippians 3:16. The rule is the law and Paul was not a sidestepper. The idea of the verb is made plain by the participle fulasswn ton nomon (keeping or observing the law).
Other Robertson's Word Pictures (NT) entries containing Acts 21:24:
Luke 1:4
Acts 18:18
Acts 21:26
Acts 21:32
Acts 24:18
Hebrews 9:10
James 4:8
1 Peter 1:22
1 John 3:3
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